Index: contrib/diff/src/diff3.c
===================================================================
--- contrib/diff/src/diff3.c
+++ contrib/diff/src/diff3.c
@@ -1406,7 +1406,7 @@
 	      line = 0;
 	      do
 		{
-		  fprintf (outputfile, line_prefix);
+		  fprintf (outputfile, "%s", line_prefix);
 		  cp = D_RELNUM (ptr, realfile, line);
 		  length = D_RELLEN (ptr, realfile, line);
 		  fwrite (cp, sizeof (char), length, outputfile);