diff --git a/src/_imagingcms.c b/src/_imagingcms.c
index 6d01770ccb2..27d5ad3b0b7 100644
--- a/src/_imagingcms.c
+++ b/src/_imagingcms.c
@@ -26,7 +26,7 @@ kevin@cazabon.com\n\
 https://www.cazabon.com\n\
 "
 
-#include "libImaging/Imaging.h"  // Include before wchar.h so _GNU_SOURCE is set
+#include "libImaging/Imaging.h"  // Set _GNU_SOURCE in Python.h before wchar.h
 
 #include <wchar.h>
 #include <datetime.h>