diff --git a/dom/bindings/Codegen.py b/dom/bindings/Codegen.py
index 886489132774..c12975673aa5 100644
--- a/dom/bindings/Codegen.py
+++ b/dom/bindings/Codegen.py
@@ -10234,10 +10234,13 @@ class CGUnionStruct(CGThing):
                         visibility="public",
                         explicit=True,
                         body="*this = aOther;\n"))
+                op_body = CGList([])
+                op_body.append(CGSwitch("aOther.mType", assignmentCases))
+                op_body.append(CGGeneric("return *this;\n"))
                 methods.append(ClassMethod(
-                    "operator=", "void",
+                    "operator=", "%s&" % selfName,
                     [Argument("const %s&" % selfName, "aOther")],
-                    body=CGSwitch("aOther.mType", assignmentCases).define()))
+                    body=op_body.define()))
                 disallowCopyConstruction = False
             else:
                 disallowCopyConstruction = True
@@ -10872,7 +10875,7 @@ class CGClass(CGThing):
                 def declare(self, cgClass):
                     name = cgClass.getNameString()
                     return ("%s(const %s&) = delete;\n"
-                            "void operator=(const %s&) = delete;\n" % (name, name, name))
+                            "%s& operator=(const %s&) = delete;\n" % (name, name, name, name))
 
             disallowedCopyConstructors = [DisallowedCopyConstructor()]
         else:
@@ -12993,8 +12996,9 @@ class CGDictionary(CGThing):
                 memberAssign = CGGeneric(
                     "%s = aOther.%s;\n" % (memberName, memberName))
             body.append(memberAssign)
+        body.append(CGGeneric("return *this;\n"))
         return ClassMethod(
-            "operator=", "void",
+            "operator=", "%s&" % self.makeClassName(self.dictionary),
             [Argument("const %s&" % self.makeClassName(self.dictionary),
                       "aOther")],
             body=body.define())