diff --git a/.changeset/tall-timers-lie.md b/.changeset/tall-timers-lie.md
new file mode 100644
index 000000000..be23450b4
--- /dev/null
+++ b/.changeset/tall-timers-lie.md
@@ -0,0 +1,5 @@
+---
+"@tma.js/sdk": patch
+---
+
+Fix invalid launch params serialization
diff --git a/packages/sdk/src/launch-params/serializeLaunchParams.ts b/packages/sdk/src/launch-params/serializeLaunchParams.ts
index 431fe3af4..2f4386ee7 100644
--- a/packages/sdk/src/launch-params/serializeLaunchParams.ts
+++ b/packages/sdk/src/launch-params/serializeLaunchParams.ts
@@ -26,7 +26,7 @@ export function serializeLaunchParams(value: LaunchParams): string {
   params.set('tgWebAppVersion', version);
 
   if (startParam) {
-    params.set('tgWebAppStartParam', version);
+    params.set('tgWebAppStartParam', startParam);
   }
 
   if (typeof showSettings === 'boolean') {