diff --git a/js/src/gdb/mozilla/Root.py b/js/src/gdb/mozilla/Root.py
index 65ef76bea7a..149bc18bd54 100644
--- a/js/src/gdb/mozilla/Root.py
+++ b/js/src/gdb/mozilla/Root.py
@@ -53,7 +53,9 @@ class EncapsulatedValue(Common):
 # Return the referent of a HeapPtr, Rooted, or Handle.
 def deref(root):
     tag = root.type.strip_typedefs().tag
-    if tag.startswith('js::HeapPtr<'):
+    if not tag:
+        raise TypeError, "Can't dereference type with no structure tag: %s" % (root.type,)
+    elif tag.startswith('js::HeapPtr<'):
         return root['value']
     elif tag.startswith('js::Rooted<'):
         return root['ptr']
diff --git a/js/src/gdb/mozilla/prettyprinters.py b/js/src/gdb/mozilla/prettyprinters.py
index 6d2271de194..02edabe9769 100644
--- a/js/src/gdb/mozilla/prettyprinters.py
+++ b/js/src/gdb/mozilla/prettyprinters.py
@@ -231,7 +231,7 @@ def lookup_for_objfile(objfile):
                 for t2 in implemented_types(t.target()):
                     if t2.code == gdb.TYPE_CODE_TYPEDEF:
                         p = check_table(ptr_printers_by_tag, str(t2))
-                    elif t2.code == gdb.TYPE_CODE_STRUCT:
+                    elif t2.code == gdb.TYPE_CODE_STRUCT and t2.tag:
                         p = check_table(ptr_printers_by_tag, t2.tag)
                     else:
                         p = None
@@ -239,7 +239,7 @@ def lookup_for_objfile(objfile):
             else:
                 if t.code == gdb.TYPE_CODE_TYPEDEF:
                     p = check_table(printers_by_tag, str(t))
-                elif t.code == gdb.TYPE_CODE_STRUCT:
+                elif t.code == gdb.TYPE_CODE_STRUCT and t.tag:
                     m = template_regexp.match(t.tag)
                     if m:
                         p = check_table(template_printers_by_tag, m.group(1))