diff --git a/loader/pthread.c b/loader/pthread.c
index b7487a0..a976c4f 100644
--- a/loader/pthread.c
+++ b/loader/pthread.c
@@ -159,7 +159,7 @@
 static void DECLSPEC_NORETURN exit_thread( struct wine_pthread_thread_info *info )
 {
     wine_ldt_free_fs( info->teb_sel );
-    munmap( info->teb_base, info->teb_size );
+    if (info->teb_size) munmap( info->teb_base, info->teb_size );
     pthread_exit( (void *)info->exit_status );
 }