diff --git a/src/transformer/descriptor/helper/helper.ts b/src/transformer/descriptor/helper/helper.ts
index cf09c0b83..08eb237e6 100644
--- a/src/transformer/descriptor/helper/helper.ts
+++ b/src/transformer/descriptor/helper/helper.ts
@@ -47,7 +47,7 @@ export namespace TypescriptHelper {
         const typeDeclaration: ts.Declaration = ts.getTypeParameterOwner(declaration);
 
         // THIS IS TO FIX A MISSING IMPLEMENTATION IN TYPESCRIPT https://github.com/microsoft/TypeScript/blob/ba5e86f1406f39e89d56d4b32fd6ff8de09a0bf3/src/compiler/utilities.ts#L5138
-        if ((typeDeclaration as Declaration).typeParameters) {
+        if (typeDeclaration && (typeDeclaration as Declaration).typeParameters) {
             return typeDeclaration;
         }
 
diff --git a/src/transformer/genericDeclaration/genericDeclaration.ts b/src/transformer/genericDeclaration/genericDeclaration.ts
index ee34c1e2f..481ce9070 100644
--- a/src/transformer/genericDeclaration/genericDeclaration.ts
+++ b/src/transformer/genericDeclaration/genericDeclaration.ts
@@ -11,6 +11,14 @@ import { GenericParameter } from './genericParameter';
 export function GenericDeclaration(scope: Scope): IGenericDeclaration {
     const generics: GenericParameter[] = [];
 
+    function isGenericProvided(node: ts.TypeReferenceNode | ts.ExpressionWithTypeArguments, index: number): boolean {
+        return !!node.typeArguments && !!node.typeArguments[index];
+    }
+
+    function getGenericTypeNode(node: ts.TypeReferenceNode | ts.ExpressionWithTypeArguments, nodeDeclaration: ts.TypeParameterDeclaration, index: number): ts.TypeNode {
+        return isGenericProvided(node, index) ? node.typeArguments[index] : nodeDeclaration.default;
+    }
+
     function addGenericParameterToExisting(
         ownerParameterDeclaration: ts.TypeParameterDeclaration,
         typeParameterDeclaration: ts.TypeParameterDeclaration,
@@ -42,11 +50,21 @@ export function GenericDeclaration(scope: Scope): IGenericDeclaration {
         addFromTypeReferenceNode(node: ts.TypeReferenceNode, declarationKey: string): void {
             const typeParameterDeclarations: ts.NodeArray<ts.TypeParameterDeclaration> = TypescriptHelper.GetParameterOfNode(node.typeName);
 
-            node.typeArguments.forEach((argument: ts.TypeNode, index: number) => {
-                const genericDescriptor: ts.Expression = GetDescriptor(argument, scope);
-                const genericParameter: GenericParameter = createGenericParameter(declarationKey, typeParameterDeclarations[index], genericDescriptor);
+            if (!typeParameterDeclarations) {
+                return;
+            }
+
+            typeParameterDeclarations.forEach((declaration: ts.TypeParameterDeclaration, index: number) => {
+                const genericTypeNode: ts.TypeNode = getGenericTypeNode(node, declaration, index);
+
+                const genericParameter: GenericParameter = createGenericParameter(
+                    declarationKey,
+                    typeParameterDeclarations[index],
+                    GetDescriptor(genericTypeNode, scope));
+
                 generics.push(genericParameter);
             });
+
         },
         addFromDeclarationExtension(
             declarationKey: string,
@@ -55,9 +73,15 @@ export function GenericDeclaration(scope: Scope): IGenericDeclaration {
             extension: ts.ExpressionWithTypeArguments): void {
             const extensionDeclarationTypeParameters: ts.NodeArray<ts.TypeParameterDeclaration> = extensionDeclaration.typeParameters;
 
-            extension.typeArguments.forEach((typeArgument: ts.TypeNode, index: number) => {
-                if (ts.isTypeReferenceNode(typeArgument)) {
-                    const typeParameterDeclaration: ts.Declaration = TypescriptHelper.GetDeclarationFromNode(typeArgument.typeName);
+            if (!extensionDeclarationTypeParameters) {
+                return;
+            }
+
+            extensionDeclarationTypeParameters.reduce((acc: GenericParameter[], declaration: ts.TypeParameterDeclaration, index: number) => {
+                const genericTypeNode: ts.TypeNode = getGenericTypeNode(extension, declaration, index);
+
+                if (ts.isTypeReferenceNode(genericTypeNode)) {
+                    const typeParameterDeclaration: ts.Declaration = TypescriptHelper.GetDeclarationFromNode(genericTypeNode.typeName);
                     if (ts.isTypeParameterDeclaration(typeParameterDeclaration)) {
                         addGenericParameterToExisting(
                             extensionDeclarationTypeParameters[index],
@@ -65,26 +89,21 @@ export function GenericDeclaration(scope: Scope): IGenericDeclaration {
                             declarationKey,
                             extensionDeclarationKey,
                         );
-                    } else {
-                        const genericParameter: GenericParameter = createGenericParameter(
-                            extensionDeclarationKey,
-                            extensionDeclarationTypeParameters[index],
-                            GetDescriptor(typeArgument, scope),
-                        );
 
-                        generics.push(genericParameter);
+                        return acc;
                     }
+                }
 
-                } else {
-                    const genericParameter: GenericParameter = createGenericParameter(
-                        extensionDeclarationKey,
-                        extensionDeclarationTypeParameters[index],
-                        GetDescriptor(typeArgument, scope),
-                    );
+                const genericParameter: GenericParameter = createGenericParameter(
+                    extensionDeclarationKey,
+                    extensionDeclarationTypeParameters[index],
+                    GetDescriptor(genericTypeNode, scope),
+                );
 
-                    generics.push(genericParameter);
-                }
-            });
+                acc.push(genericParameter);
+
+                return acc;
+            }, generics);
         },
         getExpressionForAllGenerics(): ts.ObjectLiteralExpression[] {
             return generics.map((s: GenericParameter) => {
diff --git a/src/transformer/mockFactoryCall/mockFactoryCall.ts b/src/transformer/mockFactoryCall/mockFactoryCall.ts
index 6be1a385c..b04da3378 100644
--- a/src/transformer/mockFactoryCall/mockFactoryCall.ts
+++ b/src/transformer/mockFactoryCall/mockFactoryCall.ts
@@ -28,9 +28,7 @@ export function GetMockFactoryCallIntersection(intersection: ts.IntersectionType
             const declaration: ts.Declaration = TypescriptHelper.GetDeclarationFromNode((type as ts.TypeReferenceNode).typeName);
             const declarationKey: string = MockDefiner.instance.getDeclarationKeyMap(declaration);
 
-            if (type.typeArguments) {
-                genericDeclaration.addFromTypeReferenceNode(type, declarationKey);
-            }
+            genericDeclaration.addFromTypeReferenceNode(type, declarationKey);
 
             addFromDeclarationExtensions(declaration as GenericDeclarationSupported, declarationKey, genericDeclaration);
 
@@ -74,9 +72,7 @@ function getDeclarationMockFactoryCall(declaration: ts.Declaration, typeReferenc
     const mockFactoryCall: ts.Expression = MockDefiner.instance.getMockFactoryByKey(declarationKey);
     const genericDeclaration: IGenericDeclaration = GenericDeclaration(scope);
 
-    if (typeReferenceNode.typeArguments) {
-        genericDeclaration.addFromTypeReferenceNode(typeReferenceNode, declarationKey);
-    }
+    genericDeclaration.addFromTypeReferenceNode(typeReferenceNode, declarationKey);
 
     addFromDeclarationExtensions(declaration as GenericDeclarationSupported, declarationKey, genericDeclaration);
 
@@ -93,19 +89,17 @@ function addFromDeclarationExtensions(declaration: GenericDeclarationSupported,
     if (declaration.heritageClauses) {
         declaration.heritageClauses.forEach((clause: ts.HeritageClause) => {
             clause.types.forEach((extension: ts.ExpressionWithTypeArguments) => {
-                if (extension.typeArguments) {
-                    const extensionDeclaration: ts.Declaration = TypescriptHelper.GetDeclarationFromNode(extension.expression);
+                const extensionDeclaration: ts.Declaration = TypescriptHelper.GetDeclarationFromNode(extension.expression);
 
-                    const extensionDeclarationKey: string = MockDefiner.instance.getDeclarationKeyMap(extensionDeclaration);
+                const extensionDeclarationKey: string = MockDefiner.instance.getDeclarationKeyMap(extensionDeclaration);
 
-                    genericDeclaration.addFromDeclarationExtension(
-                      declarationKey,
-                      extensionDeclaration as GenericDeclarationSupported,
-                      extensionDeclarationKey,
-                      extension);
+                genericDeclaration.addFromDeclarationExtension(
+                    declarationKey,
+                    extensionDeclaration as GenericDeclarationSupported,
+                    extensionDeclarationKey,
+                    extension);
 
-                    addFromDeclarationExtensions(extensionDeclaration as GenericDeclarationSupported, extensionDeclarationKey, genericDeclaration);
-                }
+                addFromDeclarationExtensions(extensionDeclaration as GenericDeclarationSupported, extensionDeclarationKey, genericDeclaration);
             });
         });
     }
diff --git a/test/transformer/descriptor/generic/default.test.ts b/test/transformer/descriptor/generic/default.test.ts
new file mode 100644
index 000000000..1038febdd
--- /dev/null
+++ b/test/transformer/descriptor/generic/default.test.ts
@@ -0,0 +1,49 @@
+import { createMock } from 'ts-auto-mock';
+
+describe('generic default', () => {
+    it('should assign the default value when not provided', () => {
+        interface B<P> {
+            prop: P;
+        }
+
+        interface A<P = { a: string }> extends B<P> {
+        }
+
+        const mock: A = createMock<A>();
+
+        expect(mock.prop.a).toEqual('');
+    });
+
+    it('should assign the default value of the second argument when not provided', () => {
+        interface B<P, S> {
+            prop: P;
+            prop2: S;
+        }
+
+        interface A<P = { a: string }, S = number> extends B<P, S> {
+        }
+
+        const mock: A<{ a: number }> = createMock<A<{ a: number }>>();
+
+        expect(mock.prop.a).toEqual(0);
+        expect(mock.prop2).toEqual(0);
+    });
+
+    it('should assign the default value for extension with default value', () => {
+        interface C<T> {
+            cProp: T;
+        }
+
+        interface B<P = { a: string }> extends C<P> {
+            bProp: P;
+        }
+
+        interface A extends B {
+        }
+
+        const mock: A = createMock<A>();
+
+        expect(mock.cProp.a).toEqual('');
+        expect(mock.bProp.a).toEqual('');
+    });
+});
diff --git a/test/transformer/descriptor/generic/import.ts b/test/transformer/descriptor/generic/import.test.ts
similarity index 100%
rename from test/transformer/descriptor/generic/import.ts
rename to test/transformer/descriptor/generic/import.test.ts