diff --git a/src/helpers/types.ts b/src/helpers/types.ts
index afe167a9a..7d75d63f8 100644
--- a/src/helpers/types.ts
+++ b/src/helpers/types.ts
@@ -106,7 +106,18 @@ export function convertToType(Target: any, data?: object): object | undefined {
     return data.map(item => convertToType(Target, item));
   }
 
-  return Object.assign(new Target(), data);
+  // Create instance by calling constructor to initialize instance fields
+  const instance = new (Target as any)();
+
+  // Remove undefined properties that weren't provided in the input data
+  // This prevents optional @Field() decorated properties from being enumerable
+  for (const key of Object.keys(instance)) {
+    if (instance[key] === undefined && !(key in data)) {
+      delete instance[key];
+    }
+  }
+
+  return Object.assign(instance, data);
 }
 
 export function getEnumValuesMap<T extends object>(enumObject: T) {
diff --git a/tests/functional/inputtype-enumerable-properties.ts b/tests/functional/inputtype-enumerable-properties.ts
new file mode 100644
index 000000000..3c9d6c8d3
--- /dev/null
+++ b/tests/functional/inputtype-enumerable-properties.ts
@@ -0,0 +1,168 @@
+import "reflect-metadata";
+import { type GraphQLSchema, graphql } from "graphql";
+import { Arg, Field, InputType, Query, Resolver, buildSchema } from "type-graphql";
+import { getMetadataStorage } from "@/metadata/getMetadataStorage";
+
+describe("InputType enumerable properties", () => {
+  let schema: GraphQLSchema;
+
+  beforeAll(async () => {
+    getMetadataStorage().clear();
+
+    @InputType()
+    class SampleInput {
+      @Field()
+      requiredField!: string;
+
+      @Field({ nullable: true })
+      optionalField?: string;
+
+      @Field({ nullable: true })
+      anotherOptional?: number;
+    }
+
+    @InputType()
+    class NestedInput {
+      @Field({ nullable: true })
+      optionalNested?: string;
+    }
+
+    @InputType()
+    class ParentInput {
+      @Field()
+      required!: string;
+
+      @Field(() => NestedInput, { nullable: true })
+      nested?: NestedInput;
+    }
+
+    @Resolver()
+    class SampleResolver {
+      @Query(() => String)
+      testSimpleInput(@Arg("input") input: SampleInput): string {
+        return JSON.stringify({
+          keys: Object.keys(input),
+          hasOptional: "optionalField" in input,
+          hasAnother: "anotherOptional" in input,
+          optionalValue: input.optionalField,
+        });
+      }
+
+      @Query(() => String)
+      testNestedInput(@Arg("input") input: ParentInput): string {
+        return JSON.stringify({
+          keys: Object.keys(input),
+          hasNested: "nested" in input,
+        });
+      }
+    }
+
+    schema = await buildSchema({
+      resolvers: [SampleResolver],
+      validate: false,
+    });
+  });
+
+  describe("optional fields not provided", () => {
+    it("should not create enumerable properties for undefined optional fields", async () => {
+      const query = `
+        query {
+          testSimpleInput(input: { requiredField: "test" })
+        }
+      `;
+
+      const result = await graphql({ schema, source: query });
+
+      expect(result.errors).toBeUndefined();
+      expect(result.data).toBeDefined();
+
+      const data = JSON.parse(result.data!.testSimpleInput as string);
+
+      // Only requiredField should be in Object.keys()
+      expect(data.keys).toEqual(["requiredField"]);
+
+      // Optional fields should not be enumerable
+      expect(data.hasOptional).toBe(false);
+      expect(data.hasAnother).toBe(false);
+
+      // But should still be accessible (undefined)
+      expect(data.optionalValue).toBeUndefined();
+    });
+
+    it("should handle nested InputTypes correctly", async () => {
+      const query = `
+        query {
+          testNestedInput(input: { required: "value" })
+        }
+      `;
+
+      const result = await graphql({ schema, source: query });
+
+      expect(result.errors).toBeUndefined();
+      expect(result.data).toBeDefined();
+
+      const data = JSON.parse(result.data!.testNestedInput as string);
+
+      // Only required field should be enumerable
+      expect(data.keys).toEqual(["required"]);
+
+      // Nested optional field should not be enumerable
+      expect(data.hasNested).toBe(false);
+    });
+  });
+
+  describe("optional fields provided", () => {
+    it("should include provided optional fields in Object.keys()", async () => {
+      const query = `
+        query {
+          testSimpleInput(input: { requiredField: "test", optionalField: "provided" })
+        }
+      `;
+
+      const result = await graphql({ schema, source: query });
+
+      expect(result.errors).toBeUndefined();
+      expect(result.data).toBeDefined();
+
+      const data = JSON.parse(result.data!.testSimpleInput as string);
+
+      // Both provided fields should be in Object.keys()
+      expect(data.keys).toContain("requiredField");
+      expect(data.keys).toContain("optionalField");
+
+      // Provided field should be enumerable
+      expect(data.hasOptional).toBe(true);
+
+      // Non-provided field should not be enumerable
+      expect(data.hasAnother).toBe(false);
+
+      // Value should be set
+      expect(data.optionalValue).toBe("provided");
+    });
+
+    it("should handle explicitly null values correctly", async () => {
+      const query = `
+        query {
+          testSimpleInput(input: { requiredField: "test", optionalField: null })
+        }
+      `;
+
+      const result = await graphql({ schema, source: query });
+
+      expect(result.errors).toBeUndefined();
+      expect(result.data).toBeDefined();
+
+      const data = JSON.parse(result.data!.testSimpleInput as string);
+
+      // Explicitly null field should be in Object.keys()
+      expect(data.keys).toContain("requiredField");
+      expect(data.keys).toContain("optionalField");
+
+      // Should be enumerable
+      expect(data.hasOptional).toBe(true);
+
+      // Value should be null (not undefined)
+      expect(data.optionalValue).toBeNull();
+    });
+  });
+});