diff --git a/modules/openapi-generator/src/main/resources/typescript/model/ObjectSerializer.mustache b/modules/openapi-generator/src/main/resources/typescript/model/ObjectSerializer.mustache
index 9cfa5b3475f0..714af5bbe22e 100644
--- a/modules/openapi-generator/src/main/resources/typescript/model/ObjectSerializer.mustache
+++ b/modules/openapi-generator/src/main/resources/typescript/model/ObjectSerializer.mustache
@@ -177,13 +177,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/client/echo_api/typescript/build/models/ObjectSerializer.ts b/samples/client/echo_api/typescript/build/models/ObjectSerializer.ts
index 0e7fed816336..a91cfd29d80e 100644
--- a/samples/client/echo_api/typescript/build/models/ObjectSerializer.ts
+++ b/samples/client/echo_api/typescript/build/models/ObjectSerializer.ts
@@ -185,13 +185,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/client/others/typescript/builds/array-of-lists/models/ObjectSerializer.ts b/samples/client/others/typescript/builds/array-of-lists/models/ObjectSerializer.ts
index 3d607eb960ef..d10cdbc5eff7 100644
--- a/samples/client/others/typescript/builds/array-of-lists/models/ObjectSerializer.ts
+++ b/samples/client/others/typescript/builds/array-of-lists/models/ObjectSerializer.ts
@@ -152,13 +152,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/client/others/typescript/builds/enum-single-value/models/ObjectSerializer.ts b/samples/client/others/typescript/builds/enum-single-value/models/ObjectSerializer.ts
index 15b6c13639d3..5ecf3d4ac6e7 100644
--- a/samples/client/others/typescript/builds/enum-single-value/models/ObjectSerializer.ts
+++ b/samples/client/others/typescript/builds/enum-single-value/models/ObjectSerializer.ts
@@ -154,13 +154,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/client/others/typescript/builds/null-types-simple/models/ObjectSerializer.ts b/samples/client/others/typescript/builds/null-types-simple/models/ObjectSerializer.ts
index d44f397943e3..7cde51dbea02 100644
--- a/samples/client/others/typescript/builds/null-types-simple/models/ObjectSerializer.ts
+++ b/samples/client/others/typescript/builds/null-types-simple/models/ObjectSerializer.ts
@@ -152,13 +152,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/client/others/typescript/builds/with-unique-items/models/ObjectSerializer.ts b/samples/client/others/typescript/builds/with-unique-items/models/ObjectSerializer.ts
index 6040ede547f6..1318620d22e9 100644
--- a/samples/client/others/typescript/builds/with-unique-items/models/ObjectSerializer.ts
+++ b/samples/client/others/typescript/builds/with-unique-items/models/ObjectSerializer.ts
@@ -149,13 +149,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/client/others/typescript/encode-decode/build/models/ObjectSerializer.ts b/samples/client/others/typescript/encode-decode/build/models/ObjectSerializer.ts
index 59eea6798cc5..a907494c3961 100644
--- a/samples/client/others/typescript/encode-decode/build/models/ObjectSerializer.ts
+++ b/samples/client/others/typescript/encode-decode/build/models/ObjectSerializer.ts
@@ -152,13 +152,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/openapi3/client/petstore/typescript/builds/browser/models/ObjectSerializer.ts b/samples/openapi3/client/petstore/typescript/builds/browser/models/ObjectSerializer.ts
index 2f297efed757..fe462a298a3a 100644
--- a/samples/openapi3/client/petstore/typescript/builds/browser/models/ObjectSerializer.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/browser/models/ObjectSerializer.ts
@@ -166,13 +166,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/openapi3/client/petstore/typescript/builds/composed-schemas/models/ObjectSerializer.ts b/samples/openapi3/client/petstore/typescript/builds/composed-schemas/models/ObjectSerializer.ts
index 1f3c61a072ca..46d1a1994ba7 100644
--- a/samples/openapi3/client/petstore/typescript/builds/composed-schemas/models/ObjectSerializer.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/composed-schemas/models/ObjectSerializer.ts
@@ -171,13 +171,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/openapi3/client/petstore/typescript/builds/default/models/ObjectSerializer.ts b/samples/openapi3/client/petstore/typescript/builds/default/models/ObjectSerializer.ts
index 2f297efed757..fe462a298a3a 100644
--- a/samples/openapi3/client/petstore/typescript/builds/default/models/ObjectSerializer.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/default/models/ObjectSerializer.ts
@@ -166,13 +166,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/openapi3/client/petstore/typescript/builds/deno/models/ObjectSerializer.ts b/samples/openapi3/client/petstore/typescript/builds/deno/models/ObjectSerializer.ts
index 60e339c8ae08..3f31d6689023 100644
--- a/samples/openapi3/client/petstore/typescript/builds/deno/models/ObjectSerializer.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/deno/models/ObjectSerializer.ts
@@ -166,13 +166,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/openapi3/client/petstore/typescript/builds/deno_object_params/models/ObjectSerializer.ts b/samples/openapi3/client/petstore/typescript/builds/deno_object_params/models/ObjectSerializer.ts
index 60e339c8ae08..3f31d6689023 100644
--- a/samples/openapi3/client/petstore/typescript/builds/deno_object_params/models/ObjectSerializer.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/deno_object_params/models/ObjectSerializer.ts
@@ -166,13 +166,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/openapi3/client/petstore/typescript/builds/explode-query/models/ObjectSerializer.ts b/samples/openapi3/client/petstore/typescript/builds/explode-query/models/ObjectSerializer.ts
index 97cbc6966a85..9b1bff296530 100644
--- a/samples/openapi3/client/petstore/typescript/builds/explode-query/models/ObjectSerializer.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/explode-query/models/ObjectSerializer.ts
@@ -296,13 +296,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/openapi3/client/petstore/typescript/builds/inversify/models/ObjectSerializer.ts b/samples/openapi3/client/petstore/typescript/builds/inversify/models/ObjectSerializer.ts
index 2f297efed757..fe462a298a3a 100644
--- a/samples/openapi3/client/petstore/typescript/builds/inversify/models/ObjectSerializer.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/inversify/models/ObjectSerializer.ts
@@ -166,13 +166,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/openapi3/client/petstore/typescript/builds/jquery/models/ObjectSerializer.ts b/samples/openapi3/client/petstore/typescript/builds/jquery/models/ObjectSerializer.ts
index 2f297efed757..fe462a298a3a 100644
--- a/samples/openapi3/client/petstore/typescript/builds/jquery/models/ObjectSerializer.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/jquery/models/ObjectSerializer.ts
@@ -166,13 +166,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/openapi3/client/petstore/typescript/builds/nullable-enum/models/ObjectSerializer.ts b/samples/openapi3/client/petstore/typescript/builds/nullable-enum/models/ObjectSerializer.ts
index b7087b6774a8..e02fd5f3757b 100644
--- a/samples/openapi3/client/petstore/typescript/builds/nullable-enum/models/ObjectSerializer.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/nullable-enum/models/ObjectSerializer.ts
@@ -150,13 +150,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }
diff --git a/samples/openapi3/client/petstore/typescript/builds/object_params/models/ObjectSerializer.ts b/samples/openapi3/client/petstore/typescript/builds/object_params/models/ObjectSerializer.ts
index 2f297efed757..fe462a298a3a 100644
--- a/samples/openapi3/client/petstore/typescript/builds/object_params/models/ObjectSerializer.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/object_params/models/ObjectSerializer.ts
@@ -166,13 +166,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }