diff --git a/C/iopreds.c b/C/iopreds.c
index d35ace6d1..118265965 100644
--- a/C/iopreds.c
+++ b/C/iopreds.c
@@ -3799,10 +3799,14 @@ format_has_tabs(const char *seq)
       ch = *seq++;
       if (ch == '*') {
 	ch = *seq++;
+      } else {
+	while (ch >= '0' && ch <= '9') ch = *seq++;
       }
-      if (ch == 't' || ch == '|' || ch == '@') {
+      if (ch == 't' || ch == '|' || ch == '@' || ch == '+') {
 	return TRUE;
       }
+      if (!ch)
+	return FALSE;
     }
   }
   return FALSE;
diff --git a/changes-5.1.html b/changes-5.1.html
index 1c7de6989..8d364993c 100644
--- a/changes-5.1.html
+++ b/changes-5.1.html
@@ -16,6 +16,7 @@
 
 <h2>Yap-5.1.0:</h2>
 <ul>
+<li> FIXED: format_has_tabs could miss tab signs. </li>
 <li> FIXED: plug holes in memory allocation from scanner. </li>
 <li> FIXED: instrument memory allocation use use_malloc. </li>
 <li> FIXED: adjust_cp_hbs was readjusting consumer choice-points (it