diff --git a/src/core/support/cpu_linux.c b/src/core/support/cpu_linux.c
index e0df699217b..ad82174894b 100644
--- a/src/core/support/cpu_linux.c
+++ b/src/core/support/cpu_linux.c
@@ -33,7 +33,7 @@
 
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
-#undef  /* _GNU_SOURCE */
+#endif  /* _GNU_SOURCE */
 
 #include <grpc/support/port_platform.h>