diff --git a/src/lib/definitions/callbackstate.ts b/src/lib/definitions/callbackstate.ts
index 704e37c8..2ada080d 100644
--- a/src/lib/definitions/callbackstate.ts
+++ b/src/lib/definitions/callbackstate.ts
@@ -109,7 +109,7 @@ export class Callbackstate {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Callbackstate} without deleted properties.
    */
-  normalize(): Callbackstate {
+  normalize = (): Callbackstate => {
     const clone = new Callbackstate(this);
 
     normalizeUsedForCompensationProperty(clone);
@@ -120,5 +120,5 @@ export class Callbackstate {
     setEndValueIfNoTransition(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/databasedswitch.ts b/src/lib/definitions/databasedswitch.ts
index 0cc2af93..98bb253e 100644
--- a/src/lib/definitions/databasedswitch.ts
+++ b/src/lib/definitions/databasedswitch.ts
@@ -83,7 +83,7 @@ export class Databasedswitch {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Databasedswitch} without deleted properties.
    */
-  normalize(): Databasedswitch {
+  normalize = (): Databasedswitch => {
     const clone = new Databasedswitch(this);
 
     normalizeUsedForCompensationProperty(clone);
@@ -91,5 +91,5 @@ export class Databasedswitch {
     normalizeDataConditionsProperty(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/defaultdef.ts b/src/lib/definitions/defaultdef.ts
index 6eedeef9..e64866bf 100644
--- a/src/lib/definitions/defaultdef.ts
+++ b/src/lib/definitions/defaultdef.ts
@@ -38,7 +38,7 @@ export class Defaultdef /* Default definition. Can be either a transition or end
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Defaultdef} without deleted properties.
    */
-  normalize(): Defaultdef {
+  normalize = (): Defaultdef => {
     const clone = new Defaultdef(this);
 
     normalizeEndProperty(clone);
@@ -46,5 +46,5 @@ export class Defaultdef /* Default definition. Can be either a transition or end
     setEndValueIfNoTransition(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/delaystate.ts b/src/lib/definitions/delaystate.ts
index ca99a9dd..6b655dde 100644
--- a/src/lib/definitions/delaystate.ts
+++ b/src/lib/definitions/delaystate.ts
@@ -92,7 +92,7 @@ export class Delaystate {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Delaystate} without deleted properties.
    */
-  normalize(): Delaystate {
+  normalize = (): Delaystate => {
     const clone = new Delaystate(this);
 
     normalizeUsedForCompensationProperty(clone);
@@ -101,5 +101,5 @@ export class Delaystate {
     normalizeTransitionProperty(clone);
     setEndValueIfNoTransition(clone);
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/end.ts b/src/lib/definitions/end.ts
index 80c1059e..33d8270c 100644
--- a/src/lib/definitions/end.ts
+++ b/src/lib/definitions/end.ts
@@ -44,12 +44,12 @@ export class End {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.End} without deleted properties.
    */
-  normalize(): End {
+  normalize = (): End => {
     const clone = new End(this);
 
     normalizeCompensateProperty(clone);
     normalizeTerminateProperty(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/enddatacondition.ts b/src/lib/definitions/enddatacondition.ts
index a281ee3f..6d5d8e4a 100644
--- a/src/lib/definitions/enddatacondition.ts
+++ b/src/lib/definitions/enddatacondition.ts
@@ -43,11 +43,11 @@ export class Enddatacondition {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Enddatacondition} without deleted properties.
    */
-  normalize(): Enddatacondition {
+  normalize = (): Enddatacondition => {
     const clone = new Enddatacondition(this);
 
     normalizeEndProperty(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/enddeventcondition.ts b/src/lib/definitions/enddeventcondition.ts
index ba377caf..d29dafdd 100644
--- a/src/lib/definitions/enddeventcondition.ts
+++ b/src/lib/definitions/enddeventcondition.ts
@@ -55,11 +55,11 @@ export class Enddeventcondition {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Enddeventcondition} without deleted properties.
    */
-  normalize(): Enddeventcondition {
+  normalize = (): Enddeventcondition => {
     const clone = new Enddeventcondition(this);
 
     normalizeEndProperty(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/error.ts b/src/lib/definitions/error.ts
index 5f112add..844edf5b 100644
--- a/src/lib/definitions/error.ts
+++ b/src/lib/definitions/error.ts
@@ -50,7 +50,7 @@ export class Error {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Error} without deleted properties.
    */
-  normalize(): Error {
+  normalize = (): Error => {
     const clone = new Error(this);
 
     normalizeEndProperty(clone);
@@ -59,5 +59,5 @@ export class Error {
     setEndValueIfNoTransition(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/eventbasedswitch.ts b/src/lib/definitions/eventbasedswitch.ts
index 3cf5337c..83186f24 100644
--- a/src/lib/definitions/eventbasedswitch.ts
+++ b/src/lib/definitions/eventbasedswitch.ts
@@ -90,7 +90,7 @@ export class Eventbasedswitch {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Eventbasedswitch} without deleted properties.
    */
-  normalize(): Eventbasedswitch {
+  normalize = (): Eventbasedswitch => {
     const clone = new Eventbasedswitch(this);
 
     normalizeUsedForCompensationProperty(clone);
@@ -98,5 +98,5 @@ export class Eventbasedswitch {
     normalizeEventConditionsProperty(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/eventdef.ts b/src/lib/definitions/eventdef.ts
index c9f68f78..c82d2792 100644
--- a/src/lib/definitions/eventdef.ts
+++ b/src/lib/definitions/eventdef.ts
@@ -57,11 +57,11 @@ export class Eventdef {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Eventdef} without deleted properties.
    */
-  normalize(): Eventdef {
+  normalize = (): Eventdef => {
     const clone = new Eventdef(this);
 
     normalizeKindProperty(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/eventstate.ts b/src/lib/definitions/eventstate.ts
index a60c09b0..6c7fd4a4 100644
--- a/src/lib/definitions/eventstate.ts
+++ b/src/lib/definitions/eventstate.ts
@@ -88,7 +88,7 @@ export class Eventstate /* This state is used to wait for events from event sour
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Eventstate} without deleted properties.
    */
-  normalize(): Eventstate {
+  normalize = (): Eventstate => {
     const clone = new Eventstate(this);
 
     normalizeExclusiveProperty(clone);
@@ -99,5 +99,5 @@ export class Eventstate /* This state is used to wait for events from event sour
     setEndValueIfNoTransition(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/exectimeout.ts b/src/lib/definitions/exectimeout.ts
index 6f9b1425..ff6a2fce 100644
--- a/src/lib/definitions/exectimeout.ts
+++ b/src/lib/definitions/exectimeout.ts
@@ -38,11 +38,11 @@ export class Exectimeout {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Exectimeout} without deleted properties.
    */
-  normalize(): Exectimeout {
+  normalize = (): Exectimeout => {
     const clone = new Exectimeout(this);
 
     normalizeInterruptProperty(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/foreachstate.ts b/src/lib/definitions/foreachstate.ts
index 5f98b4f9..261c4663 100644
--- a/src/lib/definitions/foreachstate.ts
+++ b/src/lib/definitions/foreachstate.ts
@@ -112,7 +112,7 @@ export class Foreachstate {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Foreachstate} without deleted properties.
    */
-  normalize(): Foreachstate {
+  normalize = (): Foreachstate => {
     const clone = new Foreachstate(this);
 
     normalizeUsedForCompensationProperty(clone);
@@ -122,5 +122,5 @@ export class Foreachstate {
     setEndValueIfNoTransition(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/function.ts b/src/lib/definitions/function.ts
index 9711cf38..df845da6 100644
--- a/src/lib/definitions/function.ts
+++ b/src/lib/definitions/function.ts
@@ -39,11 +39,12 @@ export class Function {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Function} without deleted properties.
    */
-  normalize(): Function {
+
+  normalize = (): Function => {
     const clone = new Function(this);
 
     normalizeTypeRestProperty(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/injectstate.ts b/src/lib/definitions/injectstate.ts
index 312e4e88..8031b563 100644
--- a/src/lib/definitions/injectstate.ts
+++ b/src/lib/definitions/injectstate.ts
@@ -83,7 +83,7 @@ export class Injectstate {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Injectstate} without deleted properties.
    */
-  normalize(): Injectstate {
+  normalize = (): Injectstate => {
     const clone = new Injectstate(this);
 
     normalizeUsedForCompensationProperty(clone);
@@ -93,5 +93,5 @@ export class Injectstate {
     setEndValueIfNoTransition(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/onevents.ts b/src/lib/definitions/onevents.ts
index 90d2e634..2905733f 100644
--- a/src/lib/definitions/onevents.ts
+++ b/src/lib/definitions/onevents.ts
@@ -47,11 +47,11 @@ export class Onevents {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Onevents} without deleted properties.
    */
-  normalize(): Onevents {
+  normalize = (): Onevents => {
     const clone = new Onevents(this);
 
     normalizeActionModeParallelProperty(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/operationstate.ts b/src/lib/definitions/operationstate.ts
index 9466e191..d157bfb4 100644
--- a/src/lib/definitions/operationstate.ts
+++ b/src/lib/definitions/operationstate.ts
@@ -101,7 +101,7 @@ export class Operationstate {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Operationstate} without deleted properties.
    */
-  normalize(): Operationstate {
+  normalize = (): Operationstate => {
     const clone = new Operationstate(this);
 
     normalizeActionModeSequentialProperty(clone);
@@ -112,5 +112,5 @@ export class Operationstate {
     setEndValueIfNoTransition(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/parallelstate.ts b/src/lib/definitions/parallelstate.ts
index 5b70df2e..658922bc 100644
--- a/src/lib/definitions/parallelstate.ts
+++ b/src/lib/definitions/parallelstate.ts
@@ -105,7 +105,7 @@ export class Parallelstate {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Parallelstate} without deleted properties.
    */
-  normalize(): Parallelstate {
+  normalize = (): Parallelstate => {
     const clone = new Parallelstate(this);
 
     normalizeCompletionTypeProperty(clone);
@@ -117,5 +117,5 @@ export class Parallelstate {
     setEndValueIfNoTransition(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/repeat.ts b/src/lib/definitions/repeat.ts
index 9bea2fc8..a5a70365 100644
--- a/src/lib/definitions/repeat.ts
+++ b/src/lib/definitions/repeat.ts
@@ -50,12 +50,12 @@ export class Repeat {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Repeat} without deleted properties.
    */
-  normalize(): Repeat {
+  normalize = (): Repeat => {
     const clone = new Repeat(this);
 
     normalizeContinueOnErrorProperty(clone);
     normalizeCheckBeforeProperty(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/subflowstate.ts b/src/lib/definitions/subflowstate.ts
index 719ded84..43f9e0a7 100644
--- a/src/lib/definitions/subflowstate.ts
+++ b/src/lib/definitions/subflowstate.ts
@@ -104,7 +104,7 @@ export class Subflowstate {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Subflowstate} without deleted properties.
    */
-  normalize(): Subflowstate {
+  normalize = (): Subflowstate => {
     const clone = new Subflowstate(this);
 
     normalizeUsedForCompensationProperty(clone);
@@ -119,5 +119,5 @@ export class Subflowstate {
     setEndValueIfNoTransition(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/transition.ts b/src/lib/definitions/transition.ts
index dc2c4966..2b98d52a 100644
--- a/src/lib/definitions/transition.ts
+++ b/src/lib/definitions/transition.ts
@@ -43,11 +43,11 @@ export class Transition {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Transition} without deleted properties.
    */
-  normalize(): Transition {
+  normalize = (): Transition => {
     const clone = new Transition(this);
 
     normalizeCompensateProperty(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/transitiondatacondition.ts b/src/lib/definitions/transitiondatacondition.ts
index c2700169..9400568f 100644
--- a/src/lib/definitions/transitiondatacondition.ts
+++ b/src/lib/definitions/transitiondatacondition.ts
@@ -43,11 +43,11 @@ export class Transitiondatacondition {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Transitiondatacondition} without deleted properties.
    */
-  normalize(): Transitiondatacondition {
+  normalize = (): Transitiondatacondition => {
     const clone = new Transitiondatacondition(this);
 
     normalizeTransitionProperty(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/transitioneventcondition.ts b/src/lib/definitions/transitioneventcondition.ts
index b8737508..acd73c13 100644
--- a/src/lib/definitions/transitioneventcondition.ts
+++ b/src/lib/definitions/transitioneventcondition.ts
@@ -54,11 +54,11 @@ export class Transitioneventcondition {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Transitioneventcondition} without deleted properties.
    */
-  normalize(): Transitioneventcondition {
+  normalize = (): Transitioneventcondition => {
     const clone = new Transitioneventcondition(this);
 
     normalizeTransitionProperty(clone);
 
     return clone;
-  }
+  };
 }
diff --git a/src/lib/definitions/workflow.ts b/src/lib/definitions/workflow.ts
index 48bf3b67..3378a817 100644
--- a/src/lib/definitions/workflow.ts
+++ b/src/lib/definitions/workflow.ts
@@ -97,7 +97,7 @@ export class Workflow {
    * Normalize the value of each property by recursively deleting properties whose value is equal to its default value. Does not modify the object state.
    * @returns {Specification.Workflow} without deleted properties.
    */
-  normalize(): Workflow {
+  normalize = (): Workflow => {
     const clone = new Workflow(this);
     normalizeKeepActiveProperty(clone);
 
@@ -110,7 +110,7 @@ export class Workflow {
 
     normalizeExecTimeout(clone);
     return clone;
-  }
+  };
 
   /**
    * Parses the provided string as Workflow
@@ -143,6 +143,6 @@ export class Workflow {
    */
   static toYaml(workflow: Workflow): string {
     validate('Workflow', workflow);
-    return yaml.dump(workflow.normalize());
+    return yaml.dump(JSON.parse(JSON.stringify(workflow.normalize())));
   }
 }
diff --git a/src/lib/utils.ts b/src/lib/utils.ts
index 61d134c7..90bcdfe7 100644
--- a/src/lib/utils.ts
+++ b/src/lib/utils.ts
@@ -29,7 +29,7 @@ export const validate = (typeName: string, data: any): boolean => {
     throw Error(`Validate function not defined for type '${typeName}'`);
   }
 
-  if (!validateFn(data)) {
+  if (!validateFn(JSON.parse(JSON.stringify(data)))) {
     console.warn(validateFn.errors);
     const firstError: DefinedError = (validateFn.errors as DefinedError[])[0];
     throw new Error(
diff --git a/tests/lib/utils.spec.ts b/tests/lib/utils.spec.ts
index 9e2af36b..9b0723ab 100644
--- a/tests/lib/utils.spec.ts
+++ b/tests/lib/utils.spec.ts
@@ -25,6 +25,30 @@ describe('validate', () => {
     expect(validate('End', false)).toBeTruthy('Expected function validate to return true for valid objects');
   });
 
+  it('should ignore "normalize" function as additionalProperty', () => {
+    const functionObj = {
+      name: 'function',
+      operation: 'operation',
+      type: 'rest',
+      normalize: () => {
+        //do something
+      },
+    };
+
+    expect(validate('Function', functionObj)).toBeTruthy();
+  });
+
+  it('should NOT ignore additionalProperties', () => {
+    const functionObj = {
+      name: 'function',
+      operation: 'operation',
+      type: 'rest',
+      keyAdditionalProperty: 'anyValue',
+    };
+
+    expect(() => validate('Function', functionObj)).toThrowError(/keyAdditionalProperty/);
+  });
+
   it('should throws an error if validator not found', () => {
     expect(() => validate('ValidatorNotDefined', {})).toThrowError();
   });