diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 26299645537e6..421162a07f8d5 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -34838,11 +34838,17 @@ namespace ts {
             if (constraintType && defaultType) {
                 checkTypeAssignableTo(defaultType, getTypeWithThisArgument(instantiateType(constraintType, makeUnaryTypeMapper(typeParameter, defaultType)), defaultType), node.default, Diagnostics.Type_0_does_not_satisfy_the_constraint_1);
             }
-            if (node.parent.kind === SyntaxKind.InterfaceDeclaration || node.parent.kind === SyntaxKind.ClassDeclaration || node.parent.kind === SyntaxKind.TypeAliasDeclaration) {
+            checkNodeDeferred(node);
+            addLazyDiagnostic(() => checkTypeNameIsReserved(node.name, Diagnostics.Type_parameter_name_cannot_be_0));
+        }
+
+        function checkTypeParameterDeferred(node: TypeParameterDeclaration) {
+            if (isInterfaceDeclaration(node.parent) || isClassLike(node.parent) || isTypeAliasDeclaration(node.parent)) {
+                const typeParameter = getDeclaredTypeOfTypeParameter(getSymbolOfNode(node));
                 const modifiers = getVarianceModifiers(typeParameter);
                 if (modifiers) {
                     const symbol = getSymbolOfNode(node.parent);
-                    if (node.parent.kind === SyntaxKind.TypeAliasDeclaration && !(getObjectFlags(getDeclaredTypeOfSymbol(symbol)) & (ObjectFlags.Anonymous | ObjectFlags.Mapped))) {
+                    if (isTypeAliasDeclaration(node.parent) && !(getObjectFlags(getDeclaredTypeOfSymbol(symbol)) & (ObjectFlags.Anonymous | ObjectFlags.Mapped))) {
                         error(node, Diagnostics.Variance_annotations_are_only_supported_in_type_aliases_for_object_function_constructor_and_mapped_types);
                     }
                     else if (modifiers === ModifierFlags.In || modifiers === ModifierFlags.Out) {
@@ -34855,7 +34861,6 @@ namespace ts {
                     }
                 }
             }
-            addLazyDiagnostic(() => checkTypeNameIsReserved(node.name, Diagnostics.Type_parameter_name_cannot_be_0));
         }
 
         function checkParameter(node: ParameterDeclaration) {
@@ -41354,6 +41359,9 @@ namespace ts {
                 case SyntaxKind.ClassExpression:
                     checkClassExpressionDeferred(node as ClassExpression);
                     break;
+                case SyntaxKind.TypeParameter:
+                    checkTypeParameterDeferred(node as TypeParameterDeclaration);
+                    break;
                 case SyntaxKind.JsxSelfClosingElement:
                     checkJsxSelfClosingElementDeferred(node as JsxSelfClosingElement);
                     break;
@@ -43551,8 +43559,7 @@ namespace ts {
                     case SyntaxKind.OutKeyword:
                         const inOutFlag = modifier.kind === SyntaxKind.InKeyword ? ModifierFlags.In : ModifierFlags.Out;
                         const inOutText = modifier.kind === SyntaxKind.InKeyword ? "in" : "out";
-                        if (node.kind !== SyntaxKind.TypeParameter || (node.parent.kind !== SyntaxKind.InterfaceDeclaration &&
-                            node.parent.kind !== SyntaxKind.ClassDeclaration && node.parent.kind !== SyntaxKind.TypeAliasDeclaration)) {
+                        if (node.kind !== SyntaxKind.TypeParameter || !(isInterfaceDeclaration(node.parent) || isClassLike(node.parent) || isTypeAliasDeclaration(node.parent))) {
                             return grammarErrorOnNode(modifier, Diagnostics._0_modifier_can_only_appear_on_a_type_parameter_of_a_class_interface_or_type_alias, inOutText);
                         }
                         if (flags & inOutFlag) {
diff --git a/tests/baselines/reference/varianceAnnotations.errors.txt b/tests/baselines/reference/varianceAnnotations.errors.txt
index 5cd036e723471..ee3d74ba561da 100644
--- a/tests/baselines/reference/varianceAnnotations.errors.txt
+++ b/tests/baselines/reference/varianceAnnotations.errors.txt
@@ -324,4 +324,18 @@ tests/cases/conformance/types/typeParameters/typeParameterLists/varianceAnnotati
 !!! error TS2345:           Types of property '_storedEvent' are incompatible.
 !!! error TS2345:             Type '{ type: "PLAY"; value: number; } | { type: "RESET"; }' is not assignable to type '{ type: "PLAY"; value: number; }'.
 !!! error TS2345:               Type '{ type: "RESET"; }' is not assignable to type '{ type: "PLAY"; value: number; }'.
+    
+    // Repros from #48618
+    
+    let Anon = class <out T> {
+        foo(): InstanceType<(typeof Anon<T>)> {
+            return this;
+        }
+    }
+    
+    let OuterC = class C<out T> {
+        foo(): C<T> {
+            return this;
+        }
+    }
     
\ No newline at end of file
diff --git a/tests/baselines/reference/varianceAnnotations.js b/tests/baselines/reference/varianceAnnotations.js
index 7e3fac5285ee3..aaecab6ac6803 100644
--- a/tests/baselines/reference/varianceAnnotations.js
+++ b/tests/baselines/reference/varianceAnnotations.js
@@ -159,6 +159,20 @@ interpret(machine);
 declare const qq: ActionObject<{ type: "PLAY"; value: number }>;
 
 createMachine<{ type: "PLAY"; value: number } | { type: "RESET" }>(qq);  // Error
+
+// Repros from #48618
+
+let Anon = class <out T> {
+    foo(): InstanceType<(typeof Anon<T>)> {
+        return this;
+    }
+}
+
+let OuterC = class C<out T> {
+    foo(): C<T> {
+        return this;
+    }
+}
 
 
 //// [varianceAnnotations.js]
@@ -186,6 +200,23 @@ var notString = pu; // Error
 var machine = createMachine({});
 interpret(machine);
 createMachine(qq); // Error
+// Repros from #48618
+var Anon = /** @class */ (function () {
+    function class_1() {
+    }
+    class_1.prototype.foo = function () {
+        return this;
+    };
+    return class_1;
+}());
+var OuterC = /** @class */ (function () {
+    function C() {
+    }
+    C.prototype.foo = function () {
+        return this;
+    };
+    return C;
+}());
 
 
 //// [varianceAnnotations.d.ts]
@@ -293,3 +324,13 @@ declare const qq: ActionObject<{
     type: "PLAY";
     value: number;
 }>;
+declare let Anon: {
+    new <out T>(): {
+        foo(): any;
+    };
+};
+declare let OuterC: {
+    new <out T>(): {
+        foo(): any;
+    };
+};
diff --git a/tests/baselines/reference/varianceAnnotations.symbols b/tests/baselines/reference/varianceAnnotations.symbols
index 78a5b9be39322..a000fe43e794b 100644
--- a/tests/baselines/reference/varianceAnnotations.symbols
+++ b/tests/baselines/reference/varianceAnnotations.symbols
@@ -448,3 +448,35 @@ createMachine<{ type: "PLAY"; value: number } | { type: "RESET" }>(qq);  // Erro
 >type : Symbol(type, Decl(varianceAnnotations.ts, 159, 49))
 >qq : Symbol(qq, Decl(varianceAnnotations.ts, 157, 13))
 
+// Repros from #48618
+
+let Anon = class <out T> {
+>Anon : Symbol(Anon, Decl(varianceAnnotations.ts, 163, 3))
+>T : Symbol(T, Decl(varianceAnnotations.ts, 163, 18))
+
+    foo(): InstanceType<(typeof Anon<T>)> {
+>foo : Symbol(Anon.foo, Decl(varianceAnnotations.ts, 163, 26))
+>InstanceType : Symbol(InstanceType, Decl(lib.es5.d.ts, --, --))
+>Anon : Symbol(Anon, Decl(varianceAnnotations.ts, 163, 3))
+>T : Symbol(T, Decl(varianceAnnotations.ts, 163, 18))
+
+        return this;
+>this : Symbol(Anon, Decl(varianceAnnotations.ts, 163, 10))
+    }
+}
+
+let OuterC = class C<out T> {
+>OuterC : Symbol(OuterC, Decl(varianceAnnotations.ts, 169, 3))
+>C : Symbol(C, Decl(varianceAnnotations.ts, 169, 12))
+>T : Symbol(T, Decl(varianceAnnotations.ts, 169, 21))
+
+    foo(): C<T> {
+>foo : Symbol(C.foo, Decl(varianceAnnotations.ts, 169, 29))
+>C : Symbol(C, Decl(varianceAnnotations.ts, 169, 12))
+>T : Symbol(T, Decl(varianceAnnotations.ts, 169, 21))
+
+        return this;
+>this : Symbol(C, Decl(varianceAnnotations.ts, 169, 12))
+    }
+}
+
diff --git a/tests/baselines/reference/varianceAnnotations.types b/tests/baselines/reference/varianceAnnotations.types
index e584d60a696c2..99c287766acee 100644
--- a/tests/baselines/reference/varianceAnnotations.types
+++ b/tests/baselines/reference/varianceAnnotations.types
@@ -346,3 +346,31 @@ createMachine<{ type: "PLAY"; value: number } | { type: "RESET" }>(qq);  // Erro
 >type : "RESET"
 >qq : ActionObject<{ type: "PLAY"; value: number; }>
 
+// Repros from #48618
+
+let Anon = class <out T> {
+>Anon : typeof Anon
+>class <out T> {    foo(): InstanceType<(typeof Anon<T>)> {        return this;    }} : typeof Anon
+
+    foo(): InstanceType<(typeof Anon<T>)> {
+>foo : () => InstanceType<(typeof Anon<T>)>
+>Anon : typeof Anon
+
+        return this;
+>this : this
+    }
+}
+
+let OuterC = class C<out T> {
+>OuterC : typeof C
+>class C<out T> {    foo(): C<T> {        return this;    }} : typeof C
+>C : typeof C
+
+    foo(): C<T> {
+>foo : () => C<T>
+
+        return this;
+>this : this
+    }
+}
+
diff --git a/tests/cases/conformance/types/typeParameters/typeParameterLists/varianceAnnotations.ts b/tests/cases/conformance/types/typeParameters/typeParameterLists/varianceAnnotations.ts
index 1a75b0c97a460..d2abd84ce6963 100644
--- a/tests/cases/conformance/types/typeParameters/typeParameterLists/varianceAnnotations.ts
+++ b/tests/cases/conformance/types/typeParameters/typeParameterLists/varianceAnnotations.ts
@@ -161,3 +161,17 @@ interpret(machine);
 declare const qq: ActionObject<{ type: "PLAY"; value: number }>;
 
 createMachine<{ type: "PLAY"; value: number } | { type: "RESET" }>(qq);  // Error
+
+// Repros from #48618
+
+let Anon = class <out T> {
+    foo(): InstanceType<(typeof Anon<T>)> {
+        return this;
+    }
+}
+
+let OuterC = class C<out T> {
+    foo(): C<T> {
+        return this;
+    }
+}