diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index ee05ca893c7e6..3dba3c505a85d 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -1801,6 +1801,10 @@
         "category": "Error",
         "code": 1537
     },
+    "A non-null assertion must be preceded by an identifier.": {
+        "category": "Error",
+        "code": 1538
+    },
 
     "The types of '{0}' are incompatible between these types.": {
         "category": "Error",
diff --git a/src/compiler/parser.ts b/src/compiler/parser.ts
index 23267f21866e7..968d06261b554 100644
--- a/src/compiler/parser.ts
+++ b/src/compiler/parser.ts
@@ -6451,8 +6451,12 @@ namespace Parser {
 
             if (!questionDotToken) {
                 if (token() === SyntaxKind.ExclamationToken && !scanner.hasPrecedingLineBreak()) {
+                    const start = scanner.getTokenFullStart();
                     nextToken();
                     expression = finishNode(factory.createNonNullExpression(expression), pos);
+                    if (expression.end - start !== 1) {
+                        parseErrorAt(start, expression.end, Diagnostics.A_non_null_assertion_must_be_preceded_by_an_identifier);
+                    }
                     continue;
                 }
                 const typeArguments = tryParse(parseTypeArgumentsInExpression);
diff --git a/tests/baselines/reference/parseNoWhitespaceBeforeExclamation.errors.txt b/tests/baselines/reference/parseNoWhitespaceBeforeExclamation.errors.txt
new file mode 100644
index 0000000000000..b83bb2a7d33ce
--- /dev/null
+++ b/tests/baselines/reference/parseNoWhitespaceBeforeExclamation.errors.txt
@@ -0,0 +1,42 @@
+parseNoWhitespaceBeforeExclamation.ts(3,6): error TS1538: A non-null assertion must be preceded by an identifier.
+parseNoWhitespaceBeforeExclamation.ts(4,6): error TS1538: A non-null assertion must be preceded by an identifier.
+parseNoWhitespaceBeforeExclamation.ts(5,6): error TS1538: A non-null assertion must be preceded by an identifier.
+parseNoWhitespaceBeforeExclamation.ts(6,6): error TS1538: A non-null assertion must be preceded by an identifier.
+parseNoWhitespaceBeforeExclamation.ts(7,6): error TS1538: A non-null assertion must be preceded by an identifier.
+parseNoWhitespaceBeforeExclamation.ts(8,6): error TS1538: A non-null assertion must be preceded by an identifier.
+parseNoWhitespaceBeforeExclamation.ts(9,6): error TS1538: A non-null assertion must be preceded by an identifier.
+parseNoWhitespaceBeforeExclamation.ts(10,6): error TS1538: A non-null assertion must be preceded by an identifier.
+parseNoWhitespaceBeforeExclamation.ts(11,6): error TS1538: A non-null assertion must be preceded by an identifier.
+
+
+==== parseNoWhitespaceBeforeExclamation.ts (9 errors) ====
+    declare var value: any;
+    
+    value !;
+         ~~
+!!! error TS1538: A non-null assertion must be preceded by an identifier.
+    value !instanceof String;
+         ~~
+!!! error TS1538: A non-null assertion must be preceded by an identifier.
+    value ! instanceof String
+         ~~
+!!! error TS1538: A non-null assertion must be preceded by an identifier.
+    value/* this is a comment */!instanceof String;
+         ~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS1538: A non-null assertion must be preceded by an identifier.
+    value/* this is a comment */! instanceof String;
+         ~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS1538: A non-null assertion must be preceded by an identifier.
+    value !in String;
+         ~~
+!!! error TS1538: A non-null assertion must be preceded by an identifier.
+    value ! in String
+         ~~
+!!! error TS1538: A non-null assertion must be preceded by an identifier.
+    value/* this is a comment */!in String;
+         ~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS1538: A non-null assertion must be preceded by an identifier.
+    value/* this is a comment */! in String;
+         ~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS1538: A non-null assertion must be preceded by an identifier.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/parseNoWhitespaceBeforeExclamation.js b/tests/baselines/reference/parseNoWhitespaceBeforeExclamation.js
new file mode 100644
index 0000000000000..38a32cdc7a17d
--- /dev/null
+++ b/tests/baselines/reference/parseNoWhitespaceBeforeExclamation.js
@@ -0,0 +1,26 @@
+//// [tests/cases/compiler/parseNoWhitespaceBeforeExclamation.ts] ////
+
+//// [parseNoWhitespaceBeforeExclamation.ts]
+declare var value: any;
+
+value !;
+value !instanceof String;
+value ! instanceof String
+value/* this is a comment */!instanceof String;
+value/* this is a comment */! instanceof String;
+value !in String;
+value ! in String
+value/* this is a comment */!in String;
+value/* this is a comment */! in String;
+
+
+//// [parseNoWhitespaceBeforeExclamation.js]
+value;
+value instanceof String;
+value instanceof String;
+value /* this is a comment */ instanceof String;
+value /* this is a comment */ instanceof String;
+value in String;
+value in String;
+value /* this is a comment */ in String;
+value /* this is a comment */ in String;
diff --git a/tests/baselines/reference/parseNoWhitespaceBeforeExclamation.symbols b/tests/baselines/reference/parseNoWhitespaceBeforeExclamation.symbols
new file mode 100644
index 0000000000000..4094ce3f5cba9
--- /dev/null
+++ b/tests/baselines/reference/parseNoWhitespaceBeforeExclamation.symbols
@@ -0,0 +1,41 @@
+//// [tests/cases/compiler/parseNoWhitespaceBeforeExclamation.ts] ////
+
+=== parseNoWhitespaceBeforeExclamation.ts ===
+declare var value: any;
+>value : Symbol(value, Decl(parseNoWhitespaceBeforeExclamation.ts, 0, 11))
+
+value !;
+>value : Symbol(value, Decl(parseNoWhitespaceBeforeExclamation.ts, 0, 11))
+
+value !instanceof String;
+>value : Symbol(value, Decl(parseNoWhitespaceBeforeExclamation.ts, 0, 11))
+>String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+value ! instanceof String
+>value : Symbol(value, Decl(parseNoWhitespaceBeforeExclamation.ts, 0, 11))
+>String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+value/* this is a comment */!instanceof String;
+>value : Symbol(value, Decl(parseNoWhitespaceBeforeExclamation.ts, 0, 11))
+>String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+value/* this is a comment */! instanceof String;
+>value : Symbol(value, Decl(parseNoWhitespaceBeforeExclamation.ts, 0, 11))
+>String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+value !in String;
+>value : Symbol(value, Decl(parseNoWhitespaceBeforeExclamation.ts, 0, 11))
+>String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+value ! in String
+>value : Symbol(value, Decl(parseNoWhitespaceBeforeExclamation.ts, 0, 11))
+>String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+value/* this is a comment */!in String;
+>value : Symbol(value, Decl(parseNoWhitespaceBeforeExclamation.ts, 0, 11))
+>String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+value/* this is a comment */! in String;
+>value : Symbol(value, Decl(parseNoWhitespaceBeforeExclamation.ts, 0, 11))
+>String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
diff --git a/tests/baselines/reference/parseNoWhitespaceBeforeExclamation.types b/tests/baselines/reference/parseNoWhitespaceBeforeExclamation.types
new file mode 100644
index 0000000000000..660abb5dc82ca
--- /dev/null
+++ b/tests/baselines/reference/parseNoWhitespaceBeforeExclamation.types
@@ -0,0 +1,93 @@
+//// [tests/cases/compiler/parseNoWhitespaceBeforeExclamation.ts] ////
+
+=== parseNoWhitespaceBeforeExclamation.ts ===
+declare var value: any;
+>value : any
+>      : ^^^
+
+value !;
+>value ! : any
+>        : ^^^
+>value : any
+>      : ^^^
+
+value !instanceof String;
+>value !instanceof String : boolean
+>                         : ^^^^^^^
+>value ! : any
+>        : ^^^
+>value : any
+>      : ^^^
+>String : StringConstructor
+>       : ^^^^^^^^^^^^^^^^^
+
+value ! instanceof String
+>value ! instanceof String : boolean
+>                          : ^^^^^^^
+>value ! : any
+>        : ^^^
+>value : any
+>      : ^^^
+>String : StringConstructor
+>       : ^^^^^^^^^^^^^^^^^
+
+value/* this is a comment */!instanceof String;
+>value/* this is a comment */!instanceof String : boolean
+>                                               : ^^^^^^^
+>value/* this is a comment */! : any
+>                              : ^^^
+>value : any
+>      : ^^^
+>String : StringConstructor
+>       : ^^^^^^^^^^^^^^^^^
+
+value/* this is a comment */! instanceof String;
+>value/* this is a comment */! instanceof String : boolean
+>                                                : ^^^^^^^
+>value/* this is a comment */! : any
+>                              : ^^^
+>value : any
+>      : ^^^
+>String : StringConstructor
+>       : ^^^^^^^^^^^^^^^^^
+
+value !in String;
+>value !in String : boolean
+>                 : ^^^^^^^
+>value ! : any
+>        : ^^^
+>value : any
+>      : ^^^
+>String : StringConstructor
+>       : ^^^^^^^^^^^^^^^^^
+
+value ! in String
+>value ! in String : boolean
+>                  : ^^^^^^^
+>value ! : any
+>        : ^^^
+>value : any
+>      : ^^^
+>String : StringConstructor
+>       : ^^^^^^^^^^^^^^^^^
+
+value/* this is a comment */!in String;
+>value/* this is a comment */!in String : boolean
+>                                       : ^^^^^^^
+>value/* this is a comment */! : any
+>                              : ^^^
+>value : any
+>      : ^^^
+>String : StringConstructor
+>       : ^^^^^^^^^^^^^^^^^
+
+value/* this is a comment */! in String;
+>value/* this is a comment */! in String : boolean
+>                                        : ^^^^^^^
+>value/* this is a comment */! : any
+>                              : ^^^
+>value : any
+>      : ^^^
+>String : StringConstructor
+>       : ^^^^^^^^^^^^^^^^^
+
diff --git a/tests/cases/compiler/parseNoWhitespaceBeforeExclamation.ts b/tests/cases/compiler/parseNoWhitespaceBeforeExclamation.ts
new file mode 100644
index 0000000000000..f5c7d75984d67
--- /dev/null
+++ b/tests/cases/compiler/parseNoWhitespaceBeforeExclamation.ts
@@ -0,0 +1,11 @@
+declare var value: any;
+
+value !;
+value !instanceof String;
+value ! instanceof String
+value/* this is a comment */!instanceof String;
+value/* this is a comment */! instanceof String;
+value !in String;
+value ! in String
+value/* this is a comment */!in String;
+value/* this is a comment */! in String;
diff --git a/tests/cases/fourslash/formattingNonNullAssertionOperator.ts b/tests/cases/fourslash/formattingNonNullAssertionOperator.ts
index 2d8b96daaff4d..057b8383f4d97 100644
--- a/tests/cases/fourslash/formattingNonNullAssertionOperator.ts
+++ b/tests/cases/fourslash/formattingNonNullAssertionOperator.ts
@@ -8,12 +8,12 @@
 
 format.document();
 goTo.marker("1");
-verify.currentLineContentIs("'bar'!;");
+verify.currentLineContentIs("'bar' !;");
 goTo.marker("2");
-verify.currentLineContentIs("('bar')!;");
+verify.currentLineContentIs("('bar') !;");
 goTo.marker("3");
-verify.currentLineContentIs("'bar'[1]!;");
+verify.currentLineContentIs("'bar'[1] !;");
 goTo.marker("4");
-verify.currentLineContentIs("var bar = 'bar'.foo!;");
+verify.currentLineContentIs("var bar = 'bar'.foo !;");
 goTo.marker("5");
-verify.currentLineContentIs("var foo = bar!;");
\ No newline at end of file
+verify.currentLineContentIs("var foo = bar !;");