diff --git a/libc/isystem/shared_mutex b/libc/isystem/shared_mutex
index c2e0eb759..774f05c1d 100644
--- a/libc/isystem/shared_mutex
+++ b/libc/isystem/shared_mutex
@@ -1,4 +1,4 @@
-#ifndef COSMOPOLITAN_LIBC_ISYSTEM_MUTEX_
-#define COSMOPOLITAN_LIBC_ISYSTEM_MUTEX_
+#ifndef COSMOPOLITAN_LIBC_ISYSTEM_SHARED_MUTEX_
+#define COSMOPOLITAN_LIBC_ISYSTEM_SHARED_MUTEX_
 #include "third_party/libcxx/shared_mutex"
-#endif /* COSMOPOLITAN_LIBC_ISYSTEM_MUTEX_ */
+#endif /* COSMOPOLITAN_LIBC_ISYSTEM_SHARED_MUTEX_ */