diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 9306907b418fb..38cf01ed9b9ac 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -17101,20 +17101,28 @@ namespace ts {
 
             // Find the first enclosing class that has the declaring classes of the protected constituents
             // of the property as base classes
-            const enclosingClass = forEachEnclosingClass(node, enclosingDeclaration => {
+            let enclosingClass = forEachEnclosingClass(node, enclosingDeclaration => {
                 const enclosingClass = <InterfaceType>getDeclaredTypeOfSymbol(getSymbolOfNode(enclosingDeclaration)!);
                 return isClassDerivedFromDeclaringClasses(enclosingClass, prop) ? enclosingClass : undefined;
             });
             // A protected property is accessible if the property is within the declaring class or classes derived from it
             if (!enclosingClass) {
-                error(errorNode, Diagnostics.Property_0_is_protected_and_only_accessible_within_class_1_and_its_subclasses, symbolToString(prop), typeToString(getDeclaringClass(prop) || type));
-                return false;
+                // allow PropertyAccessibility if context is in function with this parameter
+                // static member access is disallow
+                let thisParameter: ParameterDeclaration | undefined;
+                if (flags & ModifierFlags.Static || !(thisParameter = getThisParameterFromNodeContext(node)) || !thisParameter.type) {
+                    error(errorNode, Diagnostics.Property_0_is_protected_and_only_accessible_within_class_1_and_its_subclasses, symbolToString(prop), typeToString(getDeclaringClass(prop) || type));
+                    return false;
+                }
+
+                const thisType = getTypeFromTypeNode(thisParameter.type);
+                enclosingClass = ((thisType.flags & TypeFlags.TypeParameter) ? getConstraintFromTypeParameter(<TypeParameter>thisType) : thisType) as InterfaceType;
             }
             // No further restrictions for static properties
             if (flags & ModifierFlags.Static) {
                 return true;
             }
-             if (type.flags & TypeFlags.TypeParameter) {
+            if (type.flags & TypeFlags.TypeParameter) {
                 // get the original type -- represented as the type constraint of the 'this' type
                 type = (type as TypeParameter).isThisType ? getConstraintOfTypeParameter(<TypeParameter>type)! : getBaseConstraintOfType(<TypeParameter>type)!; // TODO: GH#18217 Use a different variable that's allowed to be undefined
             }
@@ -17125,6 +17133,11 @@ namespace ts {
             return true;
         }
 
+        function getThisParameterFromNodeContext (node: Node) {
+            const thisContainer = getThisContainer(node, /* includeArrowFunctions */ false);
+            return thisContainer && isFunctionLike(thisContainer) ? getThisParameter(thisContainer) : undefined;
+        }
+
         function symbolHasNonMethodDeclaration(symbol: Symbol) {
             return forEachProperty(symbol, prop => {
                 const propKind = getDeclarationKindFromSymbol(prop);
diff --git a/tests/baselines/reference/thisTypeAccessibility.errors.txt b/tests/baselines/reference/thisTypeAccessibility.errors.txt
new file mode 100644
index 0000000000000..915d6f20b8230
--- /dev/null
+++ b/tests/baselines/reference/thisTypeAccessibility.errors.txt
@@ -0,0 +1,74 @@
+tests/cases/conformance/types/thisType/thisTypeAccessibility.ts(17,10): error TS2341: Property 'p' is private and only accessible within class 'MyClass'.
+tests/cases/conformance/types/thisType/thisTypeAccessibility.ts(20,13): error TS2341: Property 'sp' is private and only accessible within class 'MyClass'.
+tests/cases/conformance/types/thisType/thisTypeAccessibility.ts(21,13): error TS2445: Property 'spp' is protected and only accessible within class 'MyClass' and its subclasses.
+tests/cases/conformance/types/thisType/thisTypeAccessibility.ts(26,10): error TS2341: Property 'p' is private and only accessible within class 'MyClass'.
+tests/cases/conformance/types/thisType/thisTypeAccessibility.ts(29,13): error TS2341: Property 'sp' is private and only accessible within class 'MyClass'.
+tests/cases/conformance/types/thisType/thisTypeAccessibility.ts(30,13): error TS2445: Property 'spp' is protected and only accessible within class 'MyClass' and its subclasses.
+tests/cases/conformance/types/thisType/thisTypeAccessibility.ts(35,10): error TS2341: Property 'p' is private and only accessible within class 'MyClass'.
+tests/cases/conformance/types/thisType/thisTypeAccessibility.ts(38,13): error TS2341: Property 'sp' is private and only accessible within class 'MyClass'.
+tests/cases/conformance/types/thisType/thisTypeAccessibility.ts(39,13): error TS2445: Property 'spp' is protected and only accessible within class 'MyClass' and its subclasses.
+
+
+==== tests/cases/conformance/types/thisType/thisTypeAccessibility.ts (9 errors) ====
+    class MyClass {
+        private p: number = 123;
+        protected pp: number = 123;
+        public ppp: number = 123;
+        private static sp: number = 123;
+        protected static spp: number = 123;
+        public static sppp: number = 123;
+    }
+    
+    interface MyClass {
+        extension1(p: number): void;
+        extension2(p: number): void;
+        extension3(p: number): void;
+    }
+    
+    MyClass.prototype.extension1 = function (this: MyClass, p: number) { 
+        this.p = p;
+             ~
+!!! error TS2341: Property 'p' is private and only accessible within class 'MyClass'.
+        this.pp = p;
+        this.ppp = p;
+        MyClass.sp = p;
+                ~~
+!!! error TS2341: Property 'sp' is private and only accessible within class 'MyClass'.
+        MyClass.spp = p;
+                ~~~
+!!! error TS2445: Property 'spp' is protected and only accessible within class 'MyClass' and its subclasses.
+        MyClass.sppp = p;
+    }
+    
+    MyClass.prototype.extension2 = function<T extends MyClass> (this: T, p: number) { 
+        this.p = p;
+             ~
+!!! error TS2341: Property 'p' is private and only accessible within class 'MyClass'.
+        this.pp = p;
+        this.ppp = p;
+        MyClass.sp = p;
+                ~~
+!!! error TS2341: Property 'sp' is private and only accessible within class 'MyClass'.
+        MyClass.spp = p;
+                ~~~
+!!! error TS2445: Property 'spp' is protected and only accessible within class 'MyClass' and its subclasses.
+        MyClass.sppp = p;
+    }
+    
+    function extension3<T extends MyClass> (this: T, p: number) { 
+        this.p = p;
+             ~
+!!! error TS2341: Property 'p' is private and only accessible within class 'MyClass'.
+        this.pp = p;
+        this.ppp = p;
+        MyClass.sp = p;
+                ~~
+!!! error TS2341: Property 'sp' is private and only accessible within class 'MyClass'.
+        MyClass.spp = p;
+                ~~~
+!!! error TS2445: Property 'spp' is protected and only accessible within class 'MyClass' and its subclasses.
+        MyClass.sppp = p;
+    }
+    
+    MyClass.prototype.extension3 = extension3;
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/thisTypeAccessibility.js b/tests/baselines/reference/thisTypeAccessibility.js
new file mode 100644
index 0000000000000..04340cebcd3ca
--- /dev/null
+++ b/tests/baselines/reference/thisTypeAccessibility.js
@@ -0,0 +1,83 @@
+//// [thisTypeAccessibility.ts]
+class MyClass {
+    private p: number = 123;
+    protected pp: number = 123;
+    public ppp: number = 123;
+    private static sp: number = 123;
+    protected static spp: number = 123;
+    public static sppp: number = 123;
+}
+
+interface MyClass {
+    extension1(p: number): void;
+    extension2(p: number): void;
+    extension3(p: number): void;
+}
+
+MyClass.prototype.extension1 = function (this: MyClass, p: number) { 
+    this.p = p;
+    this.pp = p;
+    this.ppp = p;
+    MyClass.sp = p;
+    MyClass.spp = p;
+    MyClass.sppp = p;
+}
+
+MyClass.prototype.extension2 = function<T extends MyClass> (this: T, p: number) { 
+    this.p = p;
+    this.pp = p;
+    this.ppp = p;
+    MyClass.sp = p;
+    MyClass.spp = p;
+    MyClass.sppp = p;
+}
+
+function extension3<T extends MyClass> (this: T, p: number) { 
+    this.p = p;
+    this.pp = p;
+    this.ppp = p;
+    MyClass.sp = p;
+    MyClass.spp = p;
+    MyClass.sppp = p;
+}
+
+MyClass.prototype.extension3 = extension3;
+
+
+//// [thisTypeAccessibility.js]
+var MyClass = /** @class */ (function () {
+    function MyClass() {
+        this.p = 123;
+        this.pp = 123;
+        this.ppp = 123;
+    }
+    MyClass.sp = 123;
+    MyClass.spp = 123;
+    MyClass.sppp = 123;
+    return MyClass;
+}());
+MyClass.prototype.extension1 = function (p) {
+    this.p = p;
+    this.pp = p;
+    this.ppp = p;
+    MyClass.sp = p;
+    MyClass.spp = p;
+    MyClass.sppp = p;
+};
+MyClass.prototype.extension2 = function (p) {
+    this.p = p;
+    this.pp = p;
+    this.ppp = p;
+    MyClass.sp = p;
+    MyClass.spp = p;
+    MyClass.sppp = p;
+};
+function extension3(p) {
+    this.p = p;
+    this.pp = p;
+    this.ppp = p;
+    MyClass.sp = p;
+    MyClass.spp = p;
+    MyClass.sppp = p;
+}
+MyClass.prototype.extension3 = extension3;
diff --git a/tests/baselines/reference/thisTypeAccessibility.symbols b/tests/baselines/reference/thisTypeAccessibility.symbols
new file mode 100644
index 0000000000000..bbb62fa57bc2e
--- /dev/null
+++ b/tests/baselines/reference/thisTypeAccessibility.symbols
@@ -0,0 +1,188 @@
+=== tests/cases/conformance/types/thisType/thisTypeAccessibility.ts ===
+class MyClass {
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+
+    private p: number = 123;
+>p : Symbol(MyClass.p, Decl(thisTypeAccessibility.ts, 0, 15))
+
+    protected pp: number = 123;
+>pp : Symbol(MyClass.pp, Decl(thisTypeAccessibility.ts, 1, 28))
+
+    public ppp: number = 123;
+>ppp : Symbol(MyClass.ppp, Decl(thisTypeAccessibility.ts, 2, 31))
+
+    private static sp: number = 123;
+>sp : Symbol(MyClass.sp, Decl(thisTypeAccessibility.ts, 3, 29))
+
+    protected static spp: number = 123;
+>spp : Symbol(MyClass.spp, Decl(thisTypeAccessibility.ts, 4, 36))
+
+    public static sppp: number = 123;
+>sppp : Symbol(MyClass.sppp, Decl(thisTypeAccessibility.ts, 5, 39))
+}
+
+interface MyClass {
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+
+    extension1(p: number): void;
+>extension1 : Symbol(MyClass.extension1, Decl(thisTypeAccessibility.ts, 9, 19))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 10, 15))
+
+    extension2(p: number): void;
+>extension2 : Symbol(MyClass.extension2, Decl(thisTypeAccessibility.ts, 10, 32))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 11, 15))
+
+    extension3(p: number): void;
+>extension3 : Symbol(MyClass.extension3, Decl(thisTypeAccessibility.ts, 11, 32))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 12, 15))
+}
+
+MyClass.prototype.extension1 = function (this: MyClass, p: number) { 
+>MyClass.prototype.extension1 : Symbol(MyClass.extension1, Decl(thisTypeAccessibility.ts, 9, 19))
+>MyClass.prototype : Symbol(MyClass.prototype)
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+>prototype : Symbol(MyClass.prototype)
+>extension1 : Symbol(MyClass.extension1, Decl(thisTypeAccessibility.ts, 9, 19))
+>this : Symbol(this, Decl(thisTypeAccessibility.ts, 15, 41))
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 15, 55))
+
+    this.p = p;
+>this.p : Symbol(MyClass.p, Decl(thisTypeAccessibility.ts, 0, 15))
+>this : Symbol(this, Decl(thisTypeAccessibility.ts, 15, 41))
+>p : Symbol(MyClass.p, Decl(thisTypeAccessibility.ts, 0, 15))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 15, 55))
+
+    this.pp = p;
+>this.pp : Symbol(MyClass.pp, Decl(thisTypeAccessibility.ts, 1, 28))
+>this : Symbol(this, Decl(thisTypeAccessibility.ts, 15, 41))
+>pp : Symbol(MyClass.pp, Decl(thisTypeAccessibility.ts, 1, 28))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 15, 55))
+
+    this.ppp = p;
+>this.ppp : Symbol(MyClass.ppp, Decl(thisTypeAccessibility.ts, 2, 31))
+>this : Symbol(this, Decl(thisTypeAccessibility.ts, 15, 41))
+>ppp : Symbol(MyClass.ppp, Decl(thisTypeAccessibility.ts, 2, 31))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 15, 55))
+
+    MyClass.sp = p;
+>MyClass.sp : Symbol(MyClass.sp, Decl(thisTypeAccessibility.ts, 3, 29))
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+>sp : Symbol(MyClass.sp, Decl(thisTypeAccessibility.ts, 3, 29))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 15, 55))
+
+    MyClass.spp = p;
+>MyClass.spp : Symbol(MyClass.spp, Decl(thisTypeAccessibility.ts, 4, 36))
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+>spp : Symbol(MyClass.spp, Decl(thisTypeAccessibility.ts, 4, 36))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 15, 55))
+
+    MyClass.sppp = p;
+>MyClass.sppp : Symbol(MyClass.sppp, Decl(thisTypeAccessibility.ts, 5, 39))
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+>sppp : Symbol(MyClass.sppp, Decl(thisTypeAccessibility.ts, 5, 39))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 15, 55))
+}
+
+MyClass.prototype.extension2 = function<T extends MyClass> (this: T, p: number) { 
+>MyClass.prototype.extension2 : Symbol(MyClass.extension2, Decl(thisTypeAccessibility.ts, 10, 32))
+>MyClass.prototype : Symbol(MyClass.prototype)
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+>prototype : Symbol(MyClass.prototype)
+>extension2 : Symbol(MyClass.extension2, Decl(thisTypeAccessibility.ts, 10, 32))
+>T : Symbol(T, Decl(thisTypeAccessibility.ts, 24, 40))
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+>this : Symbol(this, Decl(thisTypeAccessibility.ts, 24, 60))
+>T : Symbol(T, Decl(thisTypeAccessibility.ts, 24, 40))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 24, 68))
+
+    this.p = p;
+>this.p : Symbol(MyClass.p, Decl(thisTypeAccessibility.ts, 0, 15))
+>this : Symbol(this, Decl(thisTypeAccessibility.ts, 24, 60))
+>p : Symbol(MyClass.p, Decl(thisTypeAccessibility.ts, 0, 15))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 24, 68))
+
+    this.pp = p;
+>this.pp : Symbol(MyClass.pp, Decl(thisTypeAccessibility.ts, 1, 28))
+>this : Symbol(this, Decl(thisTypeAccessibility.ts, 24, 60))
+>pp : Symbol(MyClass.pp, Decl(thisTypeAccessibility.ts, 1, 28))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 24, 68))
+
+    this.ppp = p;
+>this.ppp : Symbol(MyClass.ppp, Decl(thisTypeAccessibility.ts, 2, 31))
+>this : Symbol(this, Decl(thisTypeAccessibility.ts, 24, 60))
+>ppp : Symbol(MyClass.ppp, Decl(thisTypeAccessibility.ts, 2, 31))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 24, 68))
+
+    MyClass.sp = p;
+>MyClass.sp : Symbol(MyClass.sp, Decl(thisTypeAccessibility.ts, 3, 29))
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+>sp : Symbol(MyClass.sp, Decl(thisTypeAccessibility.ts, 3, 29))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 24, 68))
+
+    MyClass.spp = p;
+>MyClass.spp : Symbol(MyClass.spp, Decl(thisTypeAccessibility.ts, 4, 36))
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+>spp : Symbol(MyClass.spp, Decl(thisTypeAccessibility.ts, 4, 36))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 24, 68))
+
+    MyClass.sppp = p;
+>MyClass.sppp : Symbol(MyClass.sppp, Decl(thisTypeAccessibility.ts, 5, 39))
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+>sppp : Symbol(MyClass.sppp, Decl(thisTypeAccessibility.ts, 5, 39))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 24, 68))
+}
+
+function extension3<T extends MyClass> (this: T, p: number) { 
+>extension3 : Symbol(extension3, Decl(thisTypeAccessibility.ts, 31, 1))
+>T : Symbol(T, Decl(thisTypeAccessibility.ts, 33, 20))
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+>this : Symbol(this, Decl(thisTypeAccessibility.ts, 33, 40))
+>T : Symbol(T, Decl(thisTypeAccessibility.ts, 33, 20))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 33, 48))
+
+    this.p = p;
+>this.p : Symbol(MyClass.p, Decl(thisTypeAccessibility.ts, 0, 15))
+>this : Symbol(this, Decl(thisTypeAccessibility.ts, 33, 40))
+>p : Symbol(MyClass.p, Decl(thisTypeAccessibility.ts, 0, 15))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 33, 48))
+
+    this.pp = p;
+>this.pp : Symbol(MyClass.pp, Decl(thisTypeAccessibility.ts, 1, 28))
+>this : Symbol(this, Decl(thisTypeAccessibility.ts, 33, 40))
+>pp : Symbol(MyClass.pp, Decl(thisTypeAccessibility.ts, 1, 28))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 33, 48))
+
+    this.ppp = p;
+>this.ppp : Symbol(MyClass.ppp, Decl(thisTypeAccessibility.ts, 2, 31))
+>this : Symbol(this, Decl(thisTypeAccessibility.ts, 33, 40))
+>ppp : Symbol(MyClass.ppp, Decl(thisTypeAccessibility.ts, 2, 31))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 33, 48))
+
+    MyClass.sp = p;
+>MyClass.sp : Symbol(MyClass.sp, Decl(thisTypeAccessibility.ts, 3, 29))
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+>sp : Symbol(MyClass.sp, Decl(thisTypeAccessibility.ts, 3, 29))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 33, 48))
+
+    MyClass.spp = p;
+>MyClass.spp : Symbol(MyClass.spp, Decl(thisTypeAccessibility.ts, 4, 36))
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+>spp : Symbol(MyClass.spp, Decl(thisTypeAccessibility.ts, 4, 36))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 33, 48))
+
+    MyClass.sppp = p;
+>MyClass.sppp : Symbol(MyClass.sppp, Decl(thisTypeAccessibility.ts, 5, 39))
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+>sppp : Symbol(MyClass.sppp, Decl(thisTypeAccessibility.ts, 5, 39))
+>p : Symbol(p, Decl(thisTypeAccessibility.ts, 33, 48))
+}
+
+MyClass.prototype.extension3 = extension3;
+>MyClass.prototype.extension3 : Symbol(MyClass.extension3, Decl(thisTypeAccessibility.ts, 11, 32))
+>MyClass.prototype : Symbol(MyClass.prototype)
+>MyClass : Symbol(MyClass, Decl(thisTypeAccessibility.ts, 0, 0), Decl(thisTypeAccessibility.ts, 7, 1))
+>prototype : Symbol(MyClass.prototype)
+>extension3 : Symbol(MyClass.extension3, Decl(thisTypeAccessibility.ts, 11, 32))
+>extension3 : Symbol(extension3, Decl(thisTypeAccessibility.ts, 31, 1))
+
diff --git a/tests/baselines/reference/thisTypeAccessibility.types b/tests/baselines/reference/thisTypeAccessibility.types
new file mode 100644
index 0000000000000..61e9434e4f0a5
--- /dev/null
+++ b/tests/baselines/reference/thisTypeAccessibility.types
@@ -0,0 +1,217 @@
+=== tests/cases/conformance/types/thisType/thisTypeAccessibility.ts ===
+class MyClass {
+>MyClass : MyClass
+
+    private p: number = 123;
+>p : number
+>123 : 123
+
+    protected pp: number = 123;
+>pp : number
+>123 : 123
+
+    public ppp: number = 123;
+>ppp : number
+>123 : 123
+
+    private static sp: number = 123;
+>sp : number
+>123 : 123
+
+    protected static spp: number = 123;
+>spp : number
+>123 : 123
+
+    public static sppp: number = 123;
+>sppp : number
+>123 : 123
+}
+
+interface MyClass {
+>MyClass : MyClass
+
+    extension1(p: number): void;
+>extension1 : (p: number) => void
+>p : number
+
+    extension2(p: number): void;
+>extension2 : (p: number) => void
+>p : number
+
+    extension3(p: number): void;
+>extension3 : (p: number) => void
+>p : number
+}
+
+MyClass.prototype.extension1 = function (this: MyClass, p: number) { 
+>MyClass.prototype.extension1 = function (this: MyClass, p: number) {     this.p = p;    this.pp = p;    this.ppp = p;    MyClass.sp = p;    MyClass.spp = p;    MyClass.sppp = p;} : (this: MyClass, p: number) => void
+>MyClass.prototype.extension1 : (p: number) => void
+>MyClass.prototype : MyClass
+>MyClass : typeof MyClass
+>prototype : MyClass
+>extension1 : (p: number) => void
+>function (this: MyClass, p: number) {     this.p = p;    this.pp = p;    this.ppp = p;    MyClass.sp = p;    MyClass.spp = p;    MyClass.sppp = p;} : (this: MyClass, p: number) => void
+>this : MyClass
+>MyClass : MyClass
+>p : number
+
+    this.p = p;
+>this.p = p : number
+>this.p : number
+>this : MyClass
+>p : number
+>p : number
+
+    this.pp = p;
+>this.pp = p : number
+>this.pp : number
+>this : MyClass
+>pp : number
+>p : number
+
+    this.ppp = p;
+>this.ppp = p : number
+>this.ppp : number
+>this : MyClass
+>ppp : number
+>p : number
+
+    MyClass.sp = p;
+>MyClass.sp = p : number
+>MyClass.sp : number
+>MyClass : typeof MyClass
+>sp : number
+>p : number
+
+    MyClass.spp = p;
+>MyClass.spp = p : number
+>MyClass.spp : number
+>MyClass : typeof MyClass
+>spp : number
+>p : number
+
+    MyClass.sppp = p;
+>MyClass.sppp = p : number
+>MyClass.sppp : number
+>MyClass : typeof MyClass
+>sppp : number
+>p : number
+}
+
+MyClass.prototype.extension2 = function<T extends MyClass> (this: T, p: number) { 
+>MyClass.prototype.extension2 = function<T extends MyClass> (this: T, p: number) {     this.p = p;    this.pp = p;    this.ppp = p;    MyClass.sp = p;    MyClass.spp = p;    MyClass.sppp = p;} : <T extends MyClass>(this: T, p: number) => void
+>MyClass.prototype.extension2 : (p: number) => void
+>MyClass.prototype : MyClass
+>MyClass : typeof MyClass
+>prototype : MyClass
+>extension2 : (p: number) => void
+>function<T extends MyClass> (this: T, p: number) {     this.p = p;    this.pp = p;    this.ppp = p;    MyClass.sp = p;    MyClass.spp = p;    MyClass.sppp = p;} : <T extends MyClass>(this: T, p: number) => void
+>T : T
+>MyClass : MyClass
+>this : T
+>T : T
+>p : number
+
+    this.p = p;
+>this.p = p : number
+>this.p : number
+>this : T
+>p : number
+>p : number
+
+    this.pp = p;
+>this.pp = p : number
+>this.pp : number
+>this : T
+>pp : number
+>p : number
+
+    this.ppp = p;
+>this.ppp = p : number
+>this.ppp : number
+>this : T
+>ppp : number
+>p : number
+
+    MyClass.sp = p;
+>MyClass.sp = p : number
+>MyClass.sp : number
+>MyClass : typeof MyClass
+>sp : number
+>p : number
+
+    MyClass.spp = p;
+>MyClass.spp = p : number
+>MyClass.spp : number
+>MyClass : typeof MyClass
+>spp : number
+>p : number
+
+    MyClass.sppp = p;
+>MyClass.sppp = p : number
+>MyClass.sppp : number
+>MyClass : typeof MyClass
+>sppp : number
+>p : number
+}
+
+function extension3<T extends MyClass> (this: T, p: number) { 
+>extension3 : <T extends MyClass>(this: T, p: number) => void
+>T : T
+>MyClass : MyClass
+>this : T
+>T : T
+>p : number
+
+    this.p = p;
+>this.p = p : number
+>this.p : number
+>this : T
+>p : number
+>p : number
+
+    this.pp = p;
+>this.pp = p : number
+>this.pp : number
+>this : T
+>pp : number
+>p : number
+
+    this.ppp = p;
+>this.ppp = p : number
+>this.ppp : number
+>this : T
+>ppp : number
+>p : number
+
+    MyClass.sp = p;
+>MyClass.sp = p : number
+>MyClass.sp : number
+>MyClass : typeof MyClass
+>sp : number
+>p : number
+
+    MyClass.spp = p;
+>MyClass.spp = p : number
+>MyClass.spp : number
+>MyClass : typeof MyClass
+>spp : number
+>p : number
+
+    MyClass.sppp = p;
+>MyClass.sppp = p : number
+>MyClass.sppp : number
+>MyClass : typeof MyClass
+>sppp : number
+>p : number
+}
+
+MyClass.prototype.extension3 = extension3;
+>MyClass.prototype.extension3 = extension3 : <T extends MyClass>(this: T, p: number) => void
+>MyClass.prototype.extension3 : (p: number) => void
+>MyClass.prototype : MyClass
+>MyClass : typeof MyClass
+>prototype : MyClass
+>extension3 : (p: number) => void
+>extension3 : <T extends MyClass>(this: T, p: number) => void
+
diff --git a/tests/cases/conformance/types/thisType/thisTypeAccessibility.ts b/tests/cases/conformance/types/thisType/thisTypeAccessibility.ts
new file mode 100644
index 0000000000000..6cdc9e712257c
--- /dev/null
+++ b/tests/cases/conformance/types/thisType/thisTypeAccessibility.ts
@@ -0,0 +1,43 @@
+class MyClass {
+    private p: number = 123;
+    protected pp: number = 123;
+    public ppp: number = 123;
+    private static sp: number = 123;
+    protected static spp: number = 123;
+    public static sppp: number = 123;
+}
+
+interface MyClass {
+    extension1(p: number): void;
+    extension2(p: number): void;
+    extension3(p: number): void;
+}
+
+MyClass.prototype.extension1 = function (this: MyClass, p: number) { 
+    this.p = p;
+    this.pp = p;
+    this.ppp = p;
+    MyClass.sp = p;
+    MyClass.spp = p;
+    MyClass.sppp = p;
+}
+
+MyClass.prototype.extension2 = function<T extends MyClass> (this: T, p: number) { 
+    this.p = p;
+    this.pp = p;
+    this.ppp = p;
+    MyClass.sp = p;
+    MyClass.spp = p;
+    MyClass.sppp = p;
+}
+
+function extension3<T extends MyClass> (this: T, p: number) { 
+    this.p = p;
+    this.pp = p;
+    this.ppp = p;
+    MyClass.sp = p;
+    MyClass.spp = p;
+    MyClass.sppp = p;
+}
+
+MyClass.prototype.extension3 = extension3;