diff --git a/src/Toolbar.cc b/src/Toolbar.cc
index 6d5a5ac4..b44017d4 100644
--- a/src/Toolbar.cc
+++ b/src/Toolbar.cc
@@ -43,9 +43,9 @@
 
 #include <X11/keysym.h>
 
-#ifdef    STDC_HEADERS
+#ifdef    HAVE_STRING_H
 #  include <string.h>
-#endif // STDC_HEADERS
+#endif // HAVE_STRING_H
 
 #ifdef    HAVE_STDIO_H
 #  include <stdio.h>