diff --git a/packages/playwright-core/src/client/network.ts b/packages/playwright-core/src/client/network.ts
index f5af59a88b..4bd7698016 100644
--- a/packages/playwright-core/src/client/network.ts
+++ b/packages/playwright-core/src/client/network.ts
@@ -141,7 +141,7 @@ export class Request extends ChannelOwner<channels.RequestChannel> implements ap
       return null;
 
     const contentType = this.headers()['content-type'];
-    if (contentType.startsWith('application/x-www-form-urlencoded')) {
+    if (contentType.includes('application/x-www-form-urlencoded')) {
       const entries: Record<string, string> = {};
       const parsed = new URLSearchParams(postData);
       for (const [k, v] of parsed.entries())