diff --git a/ChangeLog b/ChangeLog
index d33c22359a..a148b39fa5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2012-05-22  Paul Eggert  <eggert@cs.ucla.edu>
 
+	mktime: merge DEBUG change from gnulib
+	* time/mktime.c (mktime) [DEBUG]: #undef before #define-ing, in
+	case system <time.h> has a #define.
+
 	mktime: merge <sys/types.h> change from gnulib
 	* time/mktime.c: Do not include <sys/types.h>; no longer needed,
 	since <time.t> is now guaranteed to define time_t.
diff --git a/time/mktime.c b/time/mktime.c
index e4b3b66bc8..d0b7738dec 100644
--- a/time/mktime.c
+++ b/time/mktime.c
@@ -42,6 +42,7 @@
 # include <stdio.h>
 # include <stdlib.h>
 /* Make it work even if the system's libc has its own mktime routine.  */
+# undef mktime
 # define mktime my_mktime
 #endif /* DEBUG */