diff --git a/lib/strftime.c b/lib/strftime.c
index f3dcd77f4..6ab2be7d4 100644
--- a/lib/strftime.c
+++ b/lib/strftime.c
@@ -822,6 +822,7 @@ my_strftime (s, maxsize, format, tp ut_argument)
 	       "#define strftime rpl_strftime".  */
 # ifdef strftime
 #  undef strftime
+	    size_t strftime ();
 # endif
 
 	    *u++ = '%';