diff --git a/nob.h b/nob.h
index 2735a93..bba8b45 100644
--- a/nob.h
+++ b/nob.h
@@ -957,6 +957,7 @@ NOBDEF char *nob_win32_error_message(DWORD err);
 #endif // NOB_H_
 
 #ifdef NOB_IMPLEMENTATION
+#undef NOB_IMPLEMENTATION
 
 // This is like nob_proc_wait() but waits asynchronously. Depending on the platform ms means different thing.
 // On Windows it means timeout. On POSIX it means for how long to sleep after checking if the process exited,