diff --git a/modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache b/modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache
index 83b36941422..fef5aff07b0 100644
--- a/modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache
+++ b/modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache
@@ -252,6 +252,10 @@ export class {{classname}} extends runtime.BaseAPI {
         {{/isArray}}
         {{^isArray}}
         if (requestParameters['{{paramName}}'] != null) {
+            {{#isDateTimeType}}
+            formParams.append('{{baseName}}', (requestParameters['{{paramName}}'] as any).toISOString());
+            {{/isDateTimeType}}
+            {{^isDateTimeType}}
             {{#isPrimitiveType}}
             formParams.append('{{baseName}}', requestParameters['{{paramName}}'] as any);
             {{/isPrimitiveType}}
@@ -262,6 +266,7 @@ export class {{classname}} extends runtime.BaseAPI {
             formParams.append('{{baseName}}', new Blob([JSON.stringify(requestParameters['{{paramName}}'])], { type: "application/json", }));
             {{/withoutRuntimeChecks}}
             {{/isPrimitiveType}}
+            {{/isDateTimeType}}
         }
 
         {{/isArray}}
diff --git a/samples/client/petstore/typescript-fetch/builds/default-v3.0/apis/FakeApi.ts b/samples/client/petstore/typescript-fetch/builds/default-v3.0/apis/FakeApi.ts
index 484c15265f5..12df4e51387 100644
--- a/samples/client/petstore/typescript-fetch/builds/default-v3.0/apis/FakeApi.ts
+++ b/samples/client/petstore/typescript-fetch/builds/default-v3.0/apis/FakeApi.ts
@@ -722,7 +722,7 @@ export class FakeApi extends runtime.BaseAPI {
         }
 
         if (requestParameters['dateTime'] != null) {
-            formParams.append('dateTime', requestParameters['dateTime'] as any);
+            formParams.append('dateTime', (requestParameters['dateTime'] as any).toISOString());
         }
 
         if (requestParameters['password'] != null) {
diff --git a/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/apis/FakeApi.ts b/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/apis/FakeApi.ts
index dd1a525ac39..23e46bbf742 100644
--- a/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/apis/FakeApi.ts
+++ b/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/apis/FakeApi.ts
@@ -663,7 +663,7 @@ export class FakeApi extends runtime.BaseAPI {
         }
 
         if (requestParameters['dateTime'] != null) {
-            formParams.append('dateTime', requestParameters['dateTime'] as any);
+            formParams.append('dateTime', (requestParameters['dateTime'] as any).toISOString());
         }
 
         if (requestParameters['password'] != null) {