--- a/js/src/builtin/Stream.cpp
+++ b/js/src/builtin/Stream.cpp
@@ -2289,49 +2289,20 @@ CreateReadableStreamDefaultController(JS
 }
 
 // Streams spec, 3.8.3.
 // new ReadableStreamDefaultController( stream, underlyingSource, size,
 //                                      highWaterMark )
 bool
 ReadableStreamDefaultController::constructor(JSContext* cx, unsigned argc, Value* vp)
 {
-    CallArgs args = CallArgsFromVp(argc, vp);
-
-    if (!ThrowIfNotConstructing(cx, args, "ReadableStreamDefaultController")) {
-        return false;
-    }
-
-    // Step 1: If ! IsReadableStream(stream) is false, throw a TypeError exception.
-    HandleValue streamVal = args.get(0);
-    if (!Is<ReadableStream>(streamVal)) {
-        ReportArgTypeError(cx, "ReadableStreamDefaultController", "ReadableStream",
-                           args.get(0));
-        return false;
-    }
-
-    Rooted<ReadableStream*> stream(cx, &streamVal.toObject().as<ReadableStream>());
-
-    // Step 2: If stream.[[readableStreamController]] is not undefined, throw a
-    //         TypeError exception.
-    if (stream->hasController()) {
-        JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
-                                  JSMSG_READABLESTREAM_CONTROLLER_SET);
-        return false;
-    }
-
-    // Steps 3-11.
-    RootedObject controller(cx, CreateReadableStreamDefaultController(cx, stream, args.get(1),
-                                                                      args.get(2), args.get(3)));
-    if (!controller) {
-        return false;
-    }
-
-    args.rval().setObject(*controller);
-    return true;
+    // Step 1: Throw a TypeError.
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_BOGUS_CONSTRUCTOR, "ReadableStreamDefaultController");
+    return false;
 }
 
 static MOZ_MUST_USE double
 ReadableStreamControllerGetDesiredSizeUnchecked(ReadableStreamController* controller);
 
 // Streams spec, 3.8.4.1. get desiredSize
 // and
 // Streams spec, 3.10.4.2. get desiredSize
@@ -3219,48 +3190,20 @@ CreateReadableByteStreamController(JSCon
 }
 
 // Streams spec, 3.10.3.
 // new ReadableByteStreamController ( stream, underlyingByteSource,
 //                                    highWaterMark )
 bool
 ReadableByteStreamController::constructor(JSContext* cx, unsigned argc, Value* vp)
 {
-    CallArgs args = CallArgsFromVp(argc, vp);
-
-    if (!ThrowIfNotConstructing(cx, args, "ReadableByteStreamController")) {
-        return false;
-    }
-
-    // Step 1: If ! IsReadableStream(stream) is false, throw a TypeError exception.
-    HandleValue streamVal = args.get(0);
-    if (!Is<ReadableStream>(streamVal)) {
-        ReportArgTypeError(cx, "ReadableStreamDefaultController", "ReadableStream",
-                           args.get(0));
-        return false;
-    }
-
-    Rooted<ReadableStream*> stream(cx, &streamVal.toObject().as<ReadableStream>());
-
-    // Step 2: If stream.[[readableStreamController]] is not undefined, throw a
-    //         TypeError exception.
-    if (stream->hasController()) {
-        JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
-                                  JSMSG_READABLESTREAM_CONTROLLER_SET);
-        return false;
-    }
-
-    RootedObject controller(cx, CreateReadableByteStreamController(cx, stream, args.get(1),
-                                                                   args.get(2)));
-    if (!controller) {
-        return false;
-    }
-
-    args.rval().setObject(*controller);
-    return true;
+    // Step 1: Throw a TypeError exception.
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_BOGUS_CONSTRUCTOR, "ReadableByteStreamController");
+    return false;
 }
 
 // Version of the ReadableByteStreamConstructor that's specialized for
 // handling external, embedding-provided, underlying sources.
 static MOZ_MUST_USE ReadableByteStreamController*
 CreateReadableByteStreamController(JSContext* cx, Handle<ReadableStream*> stream,
                                    void* underlyingSource)
 {

--- a/js/src/js.msg
+++ b/js/src/js.msg
@@ -46,16 +46,17 @@ MSG_DEF(JSMSG_MORE_ARGS_NEEDED,        3
 MSG_DEF(JSMSG_INCOMPATIBLE_PROTO,      3, JSEXN_TYPEERR, "{0}.prototype.{1} called on incompatible {2}")
 MSG_DEF(JSMSG_NO_CONSTRUCTOR,          1, JSEXN_TYPEERR, "{0} has no constructor")
 MSG_DEF(JSMSG_BAD_SORT_ARG,            0, JSEXN_TYPEERR, "invalid Array.prototype.sort argument")
 MSG_DEF(JSMSG_READ_ONLY,               1, JSEXN_TYPEERR, "{0} is read-only")
 MSG_DEF(JSMSG_CANT_DELETE,             1, JSEXN_TYPEERR, "property {0} is non-configurable and can't be deleted")
 MSG_DEF(JSMSG_CANT_TRUNCATE_ARRAY,     0, JSEXN_TYPEERR, "can't delete non-configurable array element")
 MSG_DEF(JSMSG_NOT_FUNCTION,            1, JSEXN_TYPEERR, "{0} is not a function")
 MSG_DEF(JSMSG_NOT_CONSTRUCTOR,         1, JSEXN_TYPEERR, "{0} is not a constructor")
+MSG_DEF(JSMSG_BOGUS_CONSTRUCTOR,       1, JSEXN_TYPEERR, "{0} constructor can't be used directly")
 MSG_DEF(JSMSG_CANT_CONVERT_TO,         2, JSEXN_TYPEERR, "can't convert {0} to {1}")
 MSG_DEF(JSMSG_TOPRIMITIVE_NOT_CALLABLE, 2, JSEXN_TYPEERR, "can't convert {0} to {1}: its [Symbol.toPrimitive] property is not a function")
 MSG_DEF(JSMSG_TOPRIMITIVE_RETURNED_OBJECT, 2, JSEXN_TYPEERR, "can't convert {0} to {1}: its [Symbol.toPrimitive] method returned an object")
 MSG_DEF(JSMSG_NO_PROPERTIES,           1, JSEXN_TYPEERR, "{0} has no properties")
 MSG_DEF(JSMSG_PROPERTY_FAIL,           2, JSEXN_TYPEERR, "can't access property {0} of {1}")
 MSG_DEF(JSMSG_PROPERTY_FAIL_EXPR,      3, JSEXN_TYPEERR, "{0} is {1}; can't access its {2} property")
 MSG_DEF(JSMSG_ELEMENT_FAIL_EXPR,       3, JSEXN_TYPEERR, "{0} is {1}; can't access element at index {2}")
 MSG_DEF(JSMSG_BAD_REGEXP_FLAG,         1, JSEXN_SYNTAXERR, "invalid regular expression flag {0}")