diff --git a/epan/dissectors/packet-isns.c b/epan/dissectors/packet-isns.c
index 800392a27c..fe0fae65fc 100644
--- a/epan/dissectors/packet-isns.c
+++ b/epan/dissectors/packet-isns.c
@@ -880,7 +880,6 @@ AddAttribute(packet_info *pinfo, tvbuff_t *tvb, proto_tree *tree, guint offset,
             tvb, offset, 4, ENC_BIG_ENDIAN);
     offset +=4;
 
-    proto_item_set_len(attr_item, 8+len);
     proto_item_append_text(attr_item, ": %s", val_to_str_ext_const(tag, &isns_attribute_tags_ext, "Unknown"));
 
     /* it seems that an empty attribute is always valid, the original code had a similar statement */
@@ -890,6 +889,7 @@ AddAttribute(packet_info *pinfo, tvbuff_t *tvb, proto_tree *tree, guint offset,
             /* 5.6.5.1 */
             proto_tree_add_uint_format_value(tree, hf_isns_portal_group_tag, tvb, offset, 8, 0, "<NULL>");
         }
+        proto_item_set_len(attr_item, 8+len);
         return offset;
     }
 
@@ -1139,6 +1139,11 @@ AddAttribute(packet_info *pinfo, tvbuff_t *tvb, proto_tree *tree, guint offset,
             proto_tree_add_item(attr_tree, hf_isns_not_decoded_yet, tvb, offset, len, ENC_NA);
     }
 
+    /* Make sure the data is all there - and that the length won't overflow */
+    tvb_ensure_bytes_exist(tvb, offset, len);
+    /* Set the length of the item to cover only the actual item length */
+    proto_item_set_len(attr_item, 8+len);
+
     offset += len;
     return offset;
 }