diff --git a/src/os_win/thread.c b/src/os_win/thread.c
index 6ad4a71..a720433 100644
--- a/src/os_win/thread.c
+++ b/src/os_win/thread.c
@@ -61,6 +61,7 @@ typedef struct UserClosure {
 static DWORD _thread_call_user(void* arg) {
     UserClosure info = *((UserClosure*) arg);
     int result = info.func(info.arg);
+    free(arg);
     return (DWORD) result;
 }