diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 43c9818e623ad..c38e53d569dab 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -20001,7 +20001,7 @@ namespace ts {
             // Two object types that each have a property that is unmatched in the other are definitely unrelated.
             return isTupleType(source) && isTupleType(target) ? tupleTypesDefinitelyUnrelated(source, target) :
                 !!getUnmatchedProperty(source, target, /*requireOptionalProperties*/ false, /*matchDiscriminantProperties*/ true) &&
-                !!getUnmatchedProperty(target, source, /*requireOptionalProperties*/ false, /*matchDiscriminantProperties*/ true);
+                !!getUnmatchedProperty(target, source, /*requireOptionalProperties*/ false, /*matchDiscriminantProperties*/ false);
         }
 
         function getTypeFromInference(inference: InferenceInfo) {
diff --git a/tests/baselines/reference/genericRestParameters3.errors.txt b/tests/baselines/reference/genericRestParameters3.errors.txt
index 72620c41027dc..7d32573eb556c 100644
--- a/tests/baselines/reference/genericRestParameters3.errors.txt
+++ b/tests/baselines/reference/genericRestParameters3.errors.txt
@@ -23,8 +23,8 @@ tests/cases/conformance/types/rest/genericRestParameters3.ts(37,21): error TS234
     Property '0' is missing in type 'CoolArray<any>' but required in type '[cb: (...args: any[]) => void]'.
 tests/cases/conformance/types/rest/genericRestParameters3.ts(44,32): error TS2345: Argument of type '[10, 20]' is not assignable to parameter of type 'CoolArray<number>'.
   Property 'hello' is missing in type '[10, 20]' but required in type 'CoolArray<number>'.
-tests/cases/conformance/types/rest/genericRestParameters3.ts(49,1): error TS2345: Argument of type '[]' is not assignable to parameter of type 'CoolArray<unknown>'.
-  Property 'hello' is missing in type '[]' but required in type 'CoolArray<unknown>'.
+tests/cases/conformance/types/rest/genericRestParameters3.ts(49,1): error TS2345: Argument of type '[]' is not assignable to parameter of type 'CoolArray<never>'.
+  Property 'hello' is missing in type '[]' but required in type 'CoolArray<never>'.
 tests/cases/conformance/types/rest/genericRestParameters3.ts(50,5): error TS2345: Argument of type '[number]' is not assignable to parameter of type 'CoolArray<unknown>'.
   Property 'hello' is missing in type '[number]' but required in type 'CoolArray<unknown>'.
 tests/cases/conformance/types/rest/genericRestParameters3.ts(51,5): error TS2345: Argument of type '[number, number]' is not assignable to parameter of type 'CoolArray<unknown>'.
@@ -124,8 +124,8 @@ tests/cases/conformance/types/rest/genericRestParameters3.ts(59,5): error TS2345
     
     baz();       // Error
     ~~~~~
-!!! error TS2345: Argument of type '[]' is not assignable to parameter of type 'CoolArray<unknown>'.
-!!! error TS2345:   Property 'hello' is missing in type '[]' but required in type 'CoolArray<unknown>'.
+!!! error TS2345: Argument of type '[]' is not assignable to parameter of type 'CoolArray<never>'.
+!!! error TS2345:   Property 'hello' is missing in type '[]' but required in type 'CoolArray<never>'.
 !!! related TS2728 tests/cases/conformance/types/rest/genericRestParameters3.ts:30:5: 'hello' is declared here.
     baz(1);      // Error
         ~
diff --git a/tests/baselines/reference/inferenceFromIncompleteSource.errors.txt b/tests/baselines/reference/inferenceFromIncompleteSource.errors.txt
new file mode 100644
index 0000000000000..442e2253f3bae
--- /dev/null
+++ b/tests/baselines/reference/inferenceFromIncompleteSource.errors.txt
@@ -0,0 +1,21 @@
+tests/cases/compiler/inferenceFromIncompleteSource.ts(11,11): error TS2345: Argument of type '{ items: { name: string; }[]; itemKey: "name"; }' is not assignable to parameter of type 'ListProps<{ name: string; }, "name">'.
+  Property 'prop' is missing in type '{ items: { name: string; }[]; itemKey: "name"; }' but required in type 'ListProps<{ name: string; }, "name">'.
+
+
+==== tests/cases/compiler/inferenceFromIncompleteSource.ts (1 errors) ====
+    // Repro from #42030
+    
+    interface ListProps<T, K extends keyof T> {
+      items: T[];
+      itemKey: K;
+      prop: number;
+    }
+    
+    declare const Component: <T, K extends keyof T>(x: ListProps<T, K>) => void;
+    
+    Component({items: [{name:' string'}], itemKey: 'name' });
+              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2345: Argument of type '{ items: { name: string; }[]; itemKey: "name"; }' is not assignable to parameter of type 'ListProps<{ name: string; }, "name">'.
+!!! error TS2345:   Property 'prop' is missing in type '{ items: { name: string; }[]; itemKey: "name"; }' but required in type 'ListProps<{ name: string; }, "name">'.
+!!! related TS2728 tests/cases/compiler/inferenceFromIncompleteSource.ts:6:3: 'prop' is declared here.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/inferenceFromIncompleteSource.js b/tests/baselines/reference/inferenceFromIncompleteSource.js
new file mode 100644
index 0000000000000..0a668fe6c4a67
--- /dev/null
+++ b/tests/baselines/reference/inferenceFromIncompleteSource.js
@@ -0,0 +1,18 @@
+//// [inferenceFromIncompleteSource.ts]
+// Repro from #42030
+
+interface ListProps<T, K extends keyof T> {
+  items: T[];
+  itemKey: K;
+  prop: number;
+}
+
+declare const Component: <T, K extends keyof T>(x: ListProps<T, K>) => void;
+
+Component({items: [{name:' string'}], itemKey: 'name' });
+
+
+//// [inferenceFromIncompleteSource.js]
+"use strict";
+// Repro from #42030
+Component({ items: [{ name: ' string' }], itemKey: 'name' });
diff --git a/tests/baselines/reference/inferenceFromIncompleteSource.symbols b/tests/baselines/reference/inferenceFromIncompleteSource.symbols
new file mode 100644
index 0000000000000..6fb4ae1463a13
--- /dev/null
+++ b/tests/baselines/reference/inferenceFromIncompleteSource.symbols
@@ -0,0 +1,37 @@
+=== tests/cases/compiler/inferenceFromIncompleteSource.ts ===
+// Repro from #42030
+
+interface ListProps<T, K extends keyof T> {
+>ListProps : Symbol(ListProps, Decl(inferenceFromIncompleteSource.ts, 0, 0))
+>T : Symbol(T, Decl(inferenceFromIncompleteSource.ts, 2, 20))
+>K : Symbol(K, Decl(inferenceFromIncompleteSource.ts, 2, 22))
+>T : Symbol(T, Decl(inferenceFromIncompleteSource.ts, 2, 20))
+
+  items: T[];
+>items : Symbol(ListProps.items, Decl(inferenceFromIncompleteSource.ts, 2, 43))
+>T : Symbol(T, Decl(inferenceFromIncompleteSource.ts, 2, 20))
+
+  itemKey: K;
+>itemKey : Symbol(ListProps.itemKey, Decl(inferenceFromIncompleteSource.ts, 3, 13))
+>K : Symbol(K, Decl(inferenceFromIncompleteSource.ts, 2, 22))
+
+  prop: number;
+>prop : Symbol(ListProps.prop, Decl(inferenceFromIncompleteSource.ts, 4, 13))
+}
+
+declare const Component: <T, K extends keyof T>(x: ListProps<T, K>) => void;
+>Component : Symbol(Component, Decl(inferenceFromIncompleteSource.ts, 8, 13))
+>T : Symbol(T, Decl(inferenceFromIncompleteSource.ts, 8, 26))
+>K : Symbol(K, Decl(inferenceFromIncompleteSource.ts, 8, 28))
+>T : Symbol(T, Decl(inferenceFromIncompleteSource.ts, 8, 26))
+>x : Symbol(x, Decl(inferenceFromIncompleteSource.ts, 8, 48))
+>ListProps : Symbol(ListProps, Decl(inferenceFromIncompleteSource.ts, 0, 0))
+>T : Symbol(T, Decl(inferenceFromIncompleteSource.ts, 8, 26))
+>K : Symbol(K, Decl(inferenceFromIncompleteSource.ts, 8, 28))
+
+Component({items: [{name:' string'}], itemKey: 'name' });
+>Component : Symbol(Component, Decl(inferenceFromIncompleteSource.ts, 8, 13))
+>items : Symbol(items, Decl(inferenceFromIncompleteSource.ts, 10, 11))
+>name : Symbol(name, Decl(inferenceFromIncompleteSource.ts, 10, 20))
+>itemKey : Symbol(itemKey, Decl(inferenceFromIncompleteSource.ts, 10, 37))
+
diff --git a/tests/baselines/reference/inferenceFromIncompleteSource.types b/tests/baselines/reference/inferenceFromIncompleteSource.types
new file mode 100644
index 0000000000000..4ffa4f4beb833
--- /dev/null
+++ b/tests/baselines/reference/inferenceFromIncompleteSource.types
@@ -0,0 +1,30 @@
+=== tests/cases/compiler/inferenceFromIncompleteSource.ts ===
+// Repro from #42030
+
+interface ListProps<T, K extends keyof T> {
+  items: T[];
+>items : T[]
+
+  itemKey: K;
+>itemKey : K
+
+  prop: number;
+>prop : number
+}
+
+declare const Component: <T, K extends keyof T>(x: ListProps<T, K>) => void;
+>Component : <T, K extends keyof T>(x: ListProps<T, K>) => void
+>x : ListProps<T, K>
+
+Component({items: [{name:' string'}], itemKey: 'name' });
+>Component({items: [{name:' string'}], itemKey: 'name' }) : void
+>Component : <T, K extends keyof T>(x: ListProps<T, K>) => void
+>{items: [{name:' string'}], itemKey: 'name' } : { items: { name: string; }[]; itemKey: "name"; }
+>items : { name: string; }[]
+>[{name:' string'}] : { name: string; }[]
+>{name:' string'} : { name: string; }
+>name : string
+>' string' : " string"
+>itemKey : "name"
+>'name' : "name"
+
diff --git a/tests/baselines/reference/tsxStatelessFunctionComponentsWithTypeArguments4.errors.txt b/tests/baselines/reference/tsxStatelessFunctionComponentsWithTypeArguments4.errors.txt
index c79a623a24238..77dba819da7d9 100644
--- a/tests/baselines/reference/tsxStatelessFunctionComponentsWithTypeArguments4.errors.txt
+++ b/tests/baselines/reference/tsxStatelessFunctionComponentsWithTypeArguments4.errors.txt
@@ -9,9 +9,9 @@ tests/cases/conformance/jsx/file.tsx(9,14): error TS2769: No overload matches th
 tests/cases/conformance/jsx/file.tsx(10,15): error TS2769: No overload matches this call.
   Overload 1 of 3, '(): Element', gave the following error.
     Type 'T & { "ignore-prop": true; }' has no properties in common with type 'IntrinsicAttributes'.
-  Overload 2 of 3, '(attr: { b: unknown; a: string; "ignore-prop": boolean; }): Element', gave the following error.
-    Type 'T & { "ignore-prop": true; }' is not assignable to type 'IntrinsicAttributes & { b: unknown; a: string; "ignore-prop": boolean; }'.
-      Property 'a' is missing in type '{ b: number; } & { "ignore-prop": true; }' but required in type '{ b: unknown; a: string; "ignore-prop": boolean; }'.
+  Overload 2 of 3, '(attr: { b: number; a: string; "ignore-prop": boolean; }): Element', gave the following error.
+    Type 'T & { "ignore-prop": true; }' is not assignable to type 'IntrinsicAttributes & { b: number; a: string; "ignore-prop": boolean; }'.
+      Property 'a' is missing in type '{ b: number; } & { "ignore-prop": true; }' but required in type '{ b: number; a: string; "ignore-prop": boolean; }'.
   Overload 3 of 3, '(attr: { b: unknown; a: unknown; }): Element', gave the following error.
     Type 'T & { "ignore-prop": true; }' is not assignable to type 'IntrinsicAttributes & { b: unknown; a: unknown; }'.
       Property 'a' is missing in type '{ b: number; } & { "ignore-prop": true; }' but required in type '{ b: unknown; a: unknown; }'.
@@ -43,9 +43,9 @@ tests/cases/conformance/jsx/file.tsx(10,15): error TS2769: No overload matches t
 !!! error TS2769: No overload matches this call.
 !!! error TS2769:   Overload 1 of 3, '(): Element', gave the following error.
 !!! error TS2769:     Type 'T & { "ignore-prop": true; }' has no properties in common with type 'IntrinsicAttributes'.
-!!! error TS2769:   Overload 2 of 3, '(attr: { b: unknown; a: string; "ignore-prop": boolean; }): Element', gave the following error.
-!!! error TS2769:     Type 'T & { "ignore-prop": true; }' is not assignable to type 'IntrinsicAttributes & { b: unknown; a: string; "ignore-prop": boolean; }'.
-!!! error TS2769:       Property 'a' is missing in type '{ b: number; } & { "ignore-prop": true; }' but required in type '{ b: unknown; a: string; "ignore-prop": boolean; }'.
+!!! error TS2769:   Overload 2 of 3, '(attr: { b: number; a: string; "ignore-prop": boolean; }): Element', gave the following error.
+!!! error TS2769:     Type 'T & { "ignore-prop": true; }' is not assignable to type 'IntrinsicAttributes & { b: number; a: string; "ignore-prop": boolean; }'.
+!!! error TS2769:       Property 'a' is missing in type '{ b: number; } & { "ignore-prop": true; }' but required in type '{ b: number; a: string; "ignore-prop": boolean; }'.
 !!! error TS2769:   Overload 3 of 3, '(attr: { b: unknown; a: unknown; }): Element', gave the following error.
 !!! error TS2769:     Type 'T & { "ignore-prop": true; }' is not assignable to type 'IntrinsicAttributes & { b: unknown; a: unknown; }'.
 !!! error TS2769:       Property 'a' is missing in type '{ b: number; } & { "ignore-prop": true; }' but required in type '{ b: unknown; a: unknown; }'.
diff --git a/tests/cases/compiler/inferenceFromIncompleteSource.ts b/tests/cases/compiler/inferenceFromIncompleteSource.ts
new file mode 100644
index 0000000000000..7f497dd346943
--- /dev/null
+++ b/tests/cases/compiler/inferenceFromIncompleteSource.ts
@@ -0,0 +1,13 @@
+// @strict: true
+
+// Repro from #42030
+
+interface ListProps<T, K extends keyof T> {
+  items: T[];
+  itemKey: K;
+  prop: number;
+}
+
+declare const Component: <T, K extends keyof T>(x: ListProps<T, K>) => void;
+
+Component({items: [{name:' string'}], itemKey: 'name' });