diff --git a/Modules/mmapmodule.c b/Modules/mmapmodule.c
index 4b18466d280..5e8c5626353 100644
--- a/Modules/mmapmodule.c
+++ b/Modules/mmapmodule.c
@@ -16,6 +16,11 @@
  / ftp://squirl.nightmare.com/pub/python/python-ext.
 */
 
+#ifdef __linux__
+#define _GNU_SOURCE  /* So we can get MREMAP_MAYMOVE defined when
+		        sys/mman.h is included */
+#endif
+
 #include <Python.h>
 
 #ifndef MS_WIN32