diff --git a/git-compat-util.h b/git-compat-util.h
index e283c46c6fa06e..da2986e652fee7 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -201,7 +201,9 @@ DISABLE_WARNING(-Wsign-compare)
 #define _ALL_SOURCE 1
 #define _GNU_SOURCE 1
 #define _BSD_SOURCE 1
+#ifndef _DEFAULT_SOURCE
 #define _DEFAULT_SOURCE 1
+#endif
 #define _NETBSD_SOURCE 1
 #define _SGI_SOURCE 1