diff --git a/image/spec/v1.1.md b/image/spec/v1.1.md
index 181f1fb605..3a32b6bd36 100644
--- a/image/spec/v1.1.md
+++ b/image/spec/v1.1.md
@@ -87,7 +87,8 @@ This specification uses the following terms:
     <dd>
         A tag serves to map a descriptive, user-given name to any single image
         ID. Tag values are limited to the set of characters
-        <code>[a-zA-Z_0-9]</code>.
+        <code>[a-zA-Z0-9_.-]</code>, except they may not start with a <code>.</code>
+        or <code>-</code> character. Tags are limited to 127 characters.
     </dd>
     <dt>
         Repository