diff --git a/js/xpconnect/src/XPCWrappedJSClass.cpp b/js/xpconnect/src/XPCWrappedJSClass.cpp
index 09dbdcc32e3c..cf45f106a125 100644
--- a/js/xpconnect/src/XPCWrappedJSClass.cpp
+++ b/js/xpconnect/src/XPCWrappedJSClass.cpp
@@ -97,7 +97,11 @@ class MOZ_STACK_CLASS AutoSavePendingResult {
 // static
 const nsXPTInterfaceInfo* nsXPCWrappedJS::GetInterfaceInfo(REFNSIID aIID) {
   const nsXPTInterfaceInfo* info = nsXPTInterfaceInfo::ByIID(aIID);
-  if (!info || info->IsBuiltinClass()) {
+  if (!info) {
+    return nullptr;
+  }
+
+  if (info->IsBuiltinClass() || !nsXPConnect::IsISupportsDescendant(info)) {
     return nullptr;
   }
 
diff --git a/js/xpconnect/src/XPCWrappedNativeInfo.cpp b/js/xpconnect/src/XPCWrappedNativeInfo.cpp
index 620b4d34be9c..d9aebda71a71 100644
--- a/js/xpconnect/src/XPCWrappedNativeInfo.cpp
+++ b/js/xpconnect/src/XPCWrappedNativeInfo.cpp
@@ -248,6 +248,16 @@ already_AddRefed<XPCNativeInterface> XPCNativeInterface::NewInstance(
 
   uint16_t methodCount = aInfo->MethodCount();
   uint16_t constCount = aInfo->ConstantCount();
+
+  // If the interface does not have nsISupports in its inheritance chain
+  // then we know we can't reflect its methods. However, some interfaces that
+  // are used just to reflect constants are declared this way. We need to
+  // go ahead and build the thing. But, we'll ignore whatever methods it may
+  // have.
+  if (!nsXPConnect::IsISupportsDescendant(aInfo)) {
+    methodCount = 0;
+  }
+
   totalCount = methodCount + constCount;
 
   if (totalCount > MAX_LOCAL_MEMBER_COUNT) {
diff --git a/js/xpconnect/src/nsXPConnect.cpp b/js/xpconnect/src/nsXPConnect.cpp
index fc40e8d2d34e..c4c2a2a6c395 100644
--- a/js/xpconnect/src/nsXPConnect.cpp
+++ b/js/xpconnect/src/nsXPConnect.cpp
@@ -166,6 +166,11 @@ XPCJSRuntime* nsXPConnect::GetRuntimeInstance() {
   return gSelf->mRuntime;
 }
 
+// static
+bool nsXPConnect::IsISupportsDescendant(const nsXPTInterfaceInfo* info) {
+  return info && info->HasAncestor(NS_GET_IID(nsISupports));
+}
+
 void xpc::ErrorBase::Init(JSErrorBase* aReport) {
   if (!aReport->filename) {
     mFileName.SetIsVoid(true);
diff --git a/js/xpconnect/src/xpcprivate.h b/js/xpconnect/src/xpcprivate.h
index 91abad7736cd..00d4cf08fb45 100644
--- a/js/xpconnect/src/xpcprivate.h
+++ b/js/xpconnect/src/xpcprivate.h
@@ -226,6 +226,8 @@ class nsXPConnect final : public nsIXPConnect {
   static XPCJSRuntime* GetRuntimeInstance();
   XPCJSContext* GetContext() { return mContext; }
 
+  static bool IsISupportsDescendant(const nsXPTInterfaceInfo* info);
+
   static nsIScriptSecurityManager* SecurityManager() {
     MOZ_ASSERT(NS_IsMainThread());
     MOZ_ASSERT(gScriptSecurityManager);
diff --git a/xpcom/idl-parser/xpidl/rust.py b/xpcom/idl-parser/xpidl/rust.py
index 93d96b124f02..c62853976989 100644
--- a/xpcom/idl-parser/xpidl/rust.py
+++ b/xpcom/idl-parser/xpidl/rust.py
@@ -479,7 +479,12 @@ def write_interface(iface, fd):
     if iface.namemap is None:
         raise Exception("Interface was not resolved.")
 
-    assert iface.base or (iface.name == "nsISupports")
+    # if we see a base class-less type other than nsISupports, we just need
+    # to discard anything else about it other than its constants.
+    if iface.base is None and iface.name != "nsISupports":
+        assert len([m for m in iface.members
+                    if type(m) == xpidl.Attribute or type(m) == xpidl.Method]) == 0
+        return
 
     # Extract the UUID's information so that it can be written into the struct definition
     names = uuid_decoder.match(iface.attributes.uuid).groupdict()
diff --git a/xpcom/idl-parser/xpidl/rust_macros.py b/xpcom/idl-parser/xpidl/rust_macros.py
index 45b37d5f4a27..fec08e02ea8c 100644
--- a/xpcom/idl-parser/xpidl/rust_macros.py
+++ b/xpcom/idl-parser/xpidl/rust_macros.py
@@ -51,7 +51,12 @@ def write_interface(iface, fd):
     if iface.namemap is None:
         raise Exception("Interface was not resolved.")
 
-    assert iface.base or (iface.name == "nsISupports")
+    # if we see a base class-less type other than nsISupports, we just need
+    # to discard anything else about it other than its constants.
+    if iface.base is None and iface.name != "nsISupports":
+        assert len([m for m in iface.members
+                    if type(m) == xpidl.Attribute or type(m) == xpidl.Method]) == 0
+        return
 
     base = 'Some("%s")' % iface.base if iface.base is not None else 'None'
     try:
diff --git a/xpcom/idl-parser/xpidl/xpidl.py b/xpcom/idl-parser/xpidl/xpidl.py
index bcbc29814816..0834b5ab94ce 100755
--- a/xpcom/idl-parser/xpidl/xpidl.py
+++ b/xpcom/idl-parser/xpidl/xpidl.py
@@ -704,8 +704,6 @@ class Interface(object):
                 raise IDLError("interface '%s' is not builtinclass but derives from "
                                "builtinclass '%s'" %
                                (self.name, self.base), self.location)
-        elif self.name != 'nsISupports':
-            raise IDLError("Interface '%s' must inherit from nsISupports" % self.name, self.location)
 
         for member in self.members:
             member.resolve(self)