--- a/diff/diff3.c
+++ b/diff/diff3.c
@@ -1503,7 +1503,7 @@
 	      line = 0;
 	      do
 		{
-		  printf_output (line_prefix);
+		  printf_output ("%s", line_prefix);
 		  cp = D_RELNUM (ptr, realfile, line);
 		  length = D_RELLEN (ptr, realfile, line);
 		  write_output (cp, length);
--- a/src/main.c
+++ b/src/main.c
@@ -1375,7 +1375,7 @@
 {
     (void) fprintf (stderr, *cpp++, program_name, cvs_cmd_name);
     for (; *cpp; cpp++)
-	(void) fprintf (stderr, *cpp);
+	(void) fprintf (stderr, "%s", *cpp);
     exit (EXIT_FAILURE);
 }