--- a/src/cmp.c
+++ b/src/cmp.c
@@ -466,7 +466,7 @@ cmp (void)
       byte_number += first_diff;
       if (comparison_type == type_first_diff && first_diff != 0)
 	{
-	  line_number += count_newlines (buf0, first_diff);
+	  line_number += count_newlines (buf0, first_diff + 1);
 	  at_line_start = buf0[first_diff - 1] == '\n';
 	}