diff --git a/src/lib/common/rdsched.c b/src/lib/common/rdsched.c
index 57960016..88f5c6e2 100644
--- a/src/lib/common/rdsched.c
+++ b/src/lib/common/rdsched.c
@@ -30,6 +30,7 @@
  *     Markus Armbruster, 2007-2011
  */
 
+/* Required for strptime() */
 #define _XOPEN_SOURCE 500
 
 #include <config.h>