diff --git a/m4/mktime.m4 b/m4/mktime.m4
index 45d899af4..fef222256 100644
--- a/m4/mktime.m4
+++ b/m4/mktime.m4
@@ -34,6 +34,9 @@ changequote(<<, >>)dnl
 # define alarm(X) /* empty */
 #endif
 
+/* Work around redefinition to rpl_putenv by other config tests.  */
+#undef putenv
+
 static time_t time_t_max;
 
 /* Values we'll use to set the TZ environment variable.  */