diff --git a/cmake_config.h.in b/cmake_config.h.in
index eded4c71d97..f8917ba563f 100644
--- a/cmake_config.h.in
+++ b/cmake_config.h.in
@@ -5,8 +5,6 @@
  */
 #ifndef _PIO_CONFIG_
 #define _PIO_CONFIG_
-/* Set to avoid warning in intel19 compiler wrt strnlen */
-#define _GNU_SOURCE
 
 /** The major part of the version number. */
 #define PIO_VERSION_MAJOR @VERSION_MAJOR@