diff --git a/modules/openapi-generator/src/main/resources/Java/libraries/native/ApiClient.mustache b/modules/openapi-generator/src/main/resources/Java/libraries/native/ApiClient.mustache
index d38af2abb69..abdea5d8f27 100644
--- a/modules/openapi-generator/src/main/resources/Java/libraries/native/ApiClient.mustache
+++ b/modules/openapi-generator/src/main/resources/Java/libraries/native/ApiClient.mustache
@@ -18,6 +18,10 @@ import java.net.http.HttpRequest;
 import java.net.http.HttpResponse;
 import java.nio.charset.Charset;
 import java.time.Duration;
+{{#java8}}
+import java.time.OffsetDateTime;
+import java.time.format.DateTimeFormatter;
+{{/java8}}
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
@@ -57,6 +61,11 @@ public class ApiClient {
     if (value == null) {
       return "";
     }
+    {{#java8}}
+    if (value instanceof OffsetDateTime) {
+      return ((OffsetDateTime) value).format(DateTimeFormatter.ISO_OFFSET_DATE_TIME);
+    }
+    {{/java8}}
     return value.toString();
   }
 
@@ -87,7 +96,7 @@ public class ApiClient {
     if (name == null || name.isEmpty() || value == null) {
       return Collections.emptyList();
     }
-    return Collections.singletonList(new Pair(urlEncode(name), urlEncode(value.toString())));
+    return Collections.singletonList(new Pair(urlEncode(name), urlEncode(valueToString(value))));
   }
 
   /**
diff --git a/modules/openapi-generator/src/main/resources/typescript-fetch/runtime.mustache b/modules/openapi-generator/src/main/resources/typescript-fetch/runtime.mustache
index 04001417a82..3fd6265e636 100644
--- a/modules/openapi-generator/src/main/resources/typescript-fetch/runtime.mustache
+++ b/modules/openapi-generator/src/main/resources/typescript-fetch/runtime.mustache
@@ -216,6 +216,9 @@ export function querystring(params: HTTPQuery, prefix: string = ''): string {
                     .join(`&${encodeURIComponent(fullKey)}=`);
                 return `${encodeURIComponent(fullKey)}=${multiValue}`;
             }
+            if (value instanceof Date) {
+                return `${encodeURIComponent(fullKey)}=${encodeURIComponent(value.toISOString())}`;
+            }
             if (value instanceof Object) {
                 return querystring(value as HTTPQuery, fullKey);
             }
diff --git a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/ApiClient.java
index c03fab20332..ce2f5a68f61 100644
--- a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/ApiClient.java
@@ -27,6 +27,8 @@ import java.net.http.HttpRequest;
 import java.net.http.HttpResponse;
 import java.nio.charset.Charset;
 import java.time.Duration;
+import java.time.OffsetDateTime;
+import java.time.format.DateTimeFormatter;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
@@ -66,6 +68,9 @@ public class ApiClient {
     if (value == null) {
       return "";
     }
+    if (value instanceof OffsetDateTime) {
+      return ((OffsetDateTime) value).format(DateTimeFormatter.ISO_OFFSET_DATE_TIME);
+    }
     return value.toString();
   }
 
@@ -96,7 +101,7 @@ public class ApiClient {
     if (name == null || name.isEmpty() || value == null) {
       return Collections.emptyList();
     }
-    return Collections.singletonList(new Pair(urlEncode(name), urlEncode(value.toString())));
+    return Collections.singletonList(new Pair(urlEncode(name), urlEncode(valueToString(value))));
   }
 
   /**
diff --git a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/ApiClient.java b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/ApiClient.java
index c03fab20332..ce2f5a68f61 100644
--- a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/ApiClient.java
@@ -27,6 +27,8 @@ import java.net.http.HttpRequest;
 import java.net.http.HttpResponse;
 import java.nio.charset.Charset;
 import java.time.Duration;
+import java.time.OffsetDateTime;
+import java.time.format.DateTimeFormatter;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
@@ -66,6 +68,9 @@ public class ApiClient {
     if (value == null) {
       return "";
     }
+    if (value instanceof OffsetDateTime) {
+      return ((OffsetDateTime) value).format(DateTimeFormatter.ISO_OFFSET_DATE_TIME);
+    }
     return value.toString();
   }
 
@@ -96,7 +101,7 @@ public class ApiClient {
     if (name == null || name.isEmpty() || value == null) {
       return Collections.emptyList();
     }
-    return Collections.singletonList(new Pair(urlEncode(name), urlEncode(value.toString())));
+    return Collections.singletonList(new Pair(urlEncode(name), urlEncode(valueToString(value))));
   }
 
   /**
diff --git a/samples/client/petstore/typescript-fetch/builds/default-v3.0/runtime.ts b/samples/client/petstore/typescript-fetch/builds/default-v3.0/runtime.ts
index f84920e94e3..89b721d0c5d 100644
--- a/samples/client/petstore/typescript-fetch/builds/default-v3.0/runtime.ts
+++ b/samples/client/petstore/typescript-fetch/builds/default-v3.0/runtime.ts
@@ -227,6 +227,9 @@ export function querystring(params: HTTPQuery, prefix: string = ''): string {
                     .join(`&${encodeURIComponent(fullKey)}=`);
                 return `${encodeURIComponent(fullKey)}=${multiValue}`;
             }
+            if (value instanceof Date) {
+                return `${encodeURIComponent(fullKey)}=${encodeURIComponent(value.toISOString())}`;
+            }
             if (value instanceof Object) {
                 return querystring(value as HTTPQuery, fullKey);
             }
diff --git a/samples/client/petstore/typescript-fetch/builds/default/runtime.ts b/samples/client/petstore/typescript-fetch/builds/default/runtime.ts
index 87070cedb4c..3673659f277 100644
--- a/samples/client/petstore/typescript-fetch/builds/default/runtime.ts
+++ b/samples/client/petstore/typescript-fetch/builds/default/runtime.ts
@@ -227,6 +227,9 @@ export function querystring(params: HTTPQuery, prefix: string = ''): string {
                     .join(`&${encodeURIComponent(fullKey)}=`);
                 return `${encodeURIComponent(fullKey)}=${multiValue}`;
             }
+            if (value instanceof Date) {
+                return `${encodeURIComponent(fullKey)}=${encodeURIComponent(value.toISOString())}`;
+            }
             if (value instanceof Object) {
                 return querystring(value as HTTPQuery, fullKey);
             }
diff --git a/samples/client/petstore/typescript-fetch/builds/enum/runtime.ts b/samples/client/petstore/typescript-fetch/builds/enum/runtime.ts
index 533e9912b14..e04306cadcb 100644
--- a/samples/client/petstore/typescript-fetch/builds/enum/runtime.ts
+++ b/samples/client/petstore/typescript-fetch/builds/enum/runtime.ts
@@ -227,6 +227,9 @@ export function querystring(params: HTTPQuery, prefix: string = ''): string {
                     .join(`&${encodeURIComponent(fullKey)}=`);
                 return `${encodeURIComponent(fullKey)}=${multiValue}`;
             }
+            if (value instanceof Date) {
+                return `${encodeURIComponent(fullKey)}=${encodeURIComponent(value.toISOString())}`;
+            }
             if (value instanceof Object) {
                 return querystring(value as HTTPQuery, fullKey);
             }
diff --git a/samples/client/petstore/typescript-fetch/builds/es6-target/src/runtime.ts b/samples/client/petstore/typescript-fetch/builds/es6-target/src/runtime.ts
index 87070cedb4c..3673659f277 100644
--- a/samples/client/petstore/typescript-fetch/builds/es6-target/src/runtime.ts
+++ b/samples/client/petstore/typescript-fetch/builds/es6-target/src/runtime.ts
@@ -227,6 +227,9 @@ export function querystring(params: HTTPQuery, prefix: string = ''): string {
                     .join(`&${encodeURIComponent(fullKey)}=`);
                 return `${encodeURIComponent(fullKey)}=${multiValue}`;
             }
+            if (value instanceof Date) {
+                return `${encodeURIComponent(fullKey)}=${encodeURIComponent(value.toISOString())}`;
+            }
             if (value instanceof Object) {
                 return querystring(value as HTTPQuery, fullKey);
             }
diff --git a/samples/client/petstore/typescript-fetch/builds/multiple-parameters/runtime.ts b/samples/client/petstore/typescript-fetch/builds/multiple-parameters/runtime.ts
index 87070cedb4c..3673659f277 100644
--- a/samples/client/petstore/typescript-fetch/builds/multiple-parameters/runtime.ts
+++ b/samples/client/petstore/typescript-fetch/builds/multiple-parameters/runtime.ts
@@ -227,6 +227,9 @@ export function querystring(params: HTTPQuery, prefix: string = ''): string {
                     .join(`&${encodeURIComponent(fullKey)}=`);
                 return `${encodeURIComponent(fullKey)}=${multiValue}`;
             }
+            if (value instanceof Date) {
+                return `${encodeURIComponent(fullKey)}=${encodeURIComponent(value.toISOString())}`;
+            }
             if (value instanceof Object) {
                 return querystring(value as HTTPQuery, fullKey);
             }
diff --git a/samples/client/petstore/typescript-fetch/builds/prefix-parameter-interfaces/src/runtime.ts b/samples/client/petstore/typescript-fetch/builds/prefix-parameter-interfaces/src/runtime.ts
index 87070cedb4c..3673659f277 100644
--- a/samples/client/petstore/typescript-fetch/builds/prefix-parameter-interfaces/src/runtime.ts
+++ b/samples/client/petstore/typescript-fetch/builds/prefix-parameter-interfaces/src/runtime.ts
@@ -227,6 +227,9 @@ export function querystring(params: HTTPQuery, prefix: string = ''): string {
                     .join(`&${encodeURIComponent(fullKey)}=`);
                 return `${encodeURIComponent(fullKey)}=${multiValue}`;
             }
+            if (value instanceof Date) {
+                return `${encodeURIComponent(fullKey)}=${encodeURIComponent(value.toISOString())}`;
+            }
             if (value instanceof Object) {
                 return querystring(value as HTTPQuery, fullKey);
             }
diff --git a/samples/client/petstore/typescript-fetch/builds/typescript-three-plus/src/runtime.ts b/samples/client/petstore/typescript-fetch/builds/typescript-three-plus/src/runtime.ts
index 3e18bd1692c..c541d163bd4 100644
--- a/samples/client/petstore/typescript-fetch/builds/typescript-three-plus/src/runtime.ts
+++ b/samples/client/petstore/typescript-fetch/builds/typescript-three-plus/src/runtime.ts
@@ -227,6 +227,9 @@ export function querystring(params: HTTPQuery, prefix: string = ''): string {
                     .join(`&${encodeURIComponent(fullKey)}=`);
                 return `${encodeURIComponent(fullKey)}=${multiValue}`;
             }
+            if (value instanceof Date) {
+                return `${encodeURIComponent(fullKey)}=${encodeURIComponent(value.toISOString())}`;
+            }
             if (value instanceof Object) {
                 return querystring(value as HTTPQuery, fullKey);
             }
diff --git a/samples/client/petstore/typescript-fetch/builds/with-interfaces/runtime.ts b/samples/client/petstore/typescript-fetch/builds/with-interfaces/runtime.ts
index 87070cedb4c..3673659f277 100644
--- a/samples/client/petstore/typescript-fetch/builds/with-interfaces/runtime.ts
+++ b/samples/client/petstore/typescript-fetch/builds/with-interfaces/runtime.ts
@@ -227,6 +227,9 @@ export function querystring(params: HTTPQuery, prefix: string = ''): string {
                     .join(`&${encodeURIComponent(fullKey)}=`);
                 return `${encodeURIComponent(fullKey)}=${multiValue}`;
             }
+            if (value instanceof Date) {
+                return `${encodeURIComponent(fullKey)}=${encodeURIComponent(value.toISOString())}`;
+            }
             if (value instanceof Object) {
                 return querystring(value as HTTPQuery, fullKey);
             }
diff --git a/samples/client/petstore/typescript-fetch/builds/with-npm-version/src/runtime.ts b/samples/client/petstore/typescript-fetch/builds/with-npm-version/src/runtime.ts
index 87070cedb4c..3673659f277 100644
--- a/samples/client/petstore/typescript-fetch/builds/with-npm-version/src/runtime.ts
+++ b/samples/client/petstore/typescript-fetch/builds/with-npm-version/src/runtime.ts
@@ -227,6 +227,9 @@ export function querystring(params: HTTPQuery, prefix: string = ''): string {
                     .join(`&${encodeURIComponent(fullKey)}=`);
                 return `${encodeURIComponent(fullKey)}=${multiValue}`;
             }
+            if (value instanceof Date) {
+                return `${encodeURIComponent(fullKey)}=${encodeURIComponent(value.toISOString())}`;
+            }
             if (value instanceof Object) {
                 return querystring(value as HTTPQuery, fullKey);
             }
diff --git a/samples/client/petstore/typescript-fetch/builds/without-runtime-checks/src/runtime.ts b/samples/client/petstore/typescript-fetch/builds/without-runtime-checks/src/runtime.ts
index 87070cedb4c..3673659f277 100644
--- a/samples/client/petstore/typescript-fetch/builds/without-runtime-checks/src/runtime.ts
+++ b/samples/client/petstore/typescript-fetch/builds/without-runtime-checks/src/runtime.ts
@@ -227,6 +227,9 @@ export function querystring(params: HTTPQuery, prefix: string = ''): string {
                     .join(`&${encodeURIComponent(fullKey)}=`);
                 return `${encodeURIComponent(fullKey)}=${multiValue}`;
             }
+            if (value instanceof Date) {
+                return `${encodeURIComponent(fullKey)}=${encodeURIComponent(value.toISOString())}`;
+            }
             if (value instanceof Object) {
                 return querystring(value as HTTPQuery, fullKey);
             }
diff --git a/samples/openapi3/client/petstore/java/native/src/main/java/org/openapitools/client/ApiClient.java b/samples/openapi3/client/petstore/java/native/src/main/java/org/openapitools/client/ApiClient.java
index c03fab20332..ce2f5a68f61 100644
--- a/samples/openapi3/client/petstore/java/native/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/openapi3/client/petstore/java/native/src/main/java/org/openapitools/client/ApiClient.java
@@ -27,6 +27,8 @@ import java.net.http.HttpRequest;
 import java.net.http.HttpResponse;
 import java.nio.charset.Charset;
 import java.time.Duration;
+import java.time.OffsetDateTime;
+import java.time.format.DateTimeFormatter;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
@@ -66,6 +68,9 @@ public class ApiClient {
     if (value == null) {
       return "";
     }
+    if (value instanceof OffsetDateTime) {
+      return ((OffsetDateTime) value).format(DateTimeFormatter.ISO_OFFSET_DATE_TIME);
+    }
     return value.toString();
   }
 
@@ -96,7 +101,7 @@ public class ApiClient {
     if (name == null || name.isEmpty() || value == null) {
       return Collections.emptyList();
     }
-    return Collections.singletonList(new Pair(urlEncode(name), urlEncode(value.toString())));
+    return Collections.singletonList(new Pair(urlEncode(name), urlEncode(valueToString(value))));
   }
 
   /**