diff --git a/src/xdisp.c b/src/xdisp.c
index fc9a11a4cc2..88f9e9c55cd 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -2961,8 +2961,11 @@ decode_mode_spec (w, c, maxwidth)
       return "-";
 
     case '+':
+      /* This differs from %* only for a modified read-only buffer.  */
       if (MODIFF > current_buffer->save_modified)
 	return "*";
+      if (!NILP (current_buffer->read_only))
+	return "%";
       return "-";
 
     case 's':