diff --git a/js/src/vm/Interpreter.cpp b/js/src/vm/Interpreter.cpp
index 623aac1b1b5c..af26f8929bb3 100644
--- a/js/src/vm/Interpreter.cpp
+++ b/js/src/vm/Interpreter.cpp
@@ -1650,7 +1650,6 @@ CASE(EnableInterruptsPseudoOpcode)
 /* Various 1-byte no-ops. */
 CASE(JSOP_NOP)
 CASE(JSOP_UNUSED2)
-CASE(JSOP_UNUSED52)
 CASE(JSOP_UNUSED83)
 CASE(JSOP_UNUSED92)
 CASE(JSOP_UNUSED103)
@@ -3559,6 +3558,24 @@ CASE(JSOP_CLASSHERITAGE)
 }
 END_CASE(JSOP_CLASSHERITAGE)
 
+CASE(JSOP_FUNWITHPROTO)
+{
+    RootedObject &proto = rootObject1;
+    proto = &REGS.sp[-1].toObject();
+
+    /* Load the specified function object literal. */
+    RootedFunction &fun = rootFunction0;
+    fun = script->getFunction(GET_UINT32_INDEX(REGS.pc));
+
+    JSObject *obj = CloneFunctionObjectIfNotSingleton(cx, fun, REGS.fp()->scopeChain(),
+                                                      proto, GenericObject);
+    if (!obj)
+        goto error;
+
+    REGS.sp[-1].setObject(*obj);
+}
+END_CASE(JSOP_FUNWITHPROTO)
+
 DEFAULT()
 {
     char numBuf[12];
diff --git a/js/src/vm/Opcodes.h b/js/src/vm/Opcodes.h
index 80168ac22c1c..0d112064e10c 100644
--- a/js/src/vm/Opcodes.h
+++ b/js/src/vm/Opcodes.h
@@ -489,7 +489,14 @@
      *   Stack: heritage => objProto, funcProto
      */ \
     macro(JSOP_CLASSHERITAGE,  51, "classheritage",   NULL,         1,  1,  2,  JOF_BYTE) \
-    macro(JSOP_UNUSED52,  52, "unused52",   NULL,         1,  0,  0,  JOF_BYTE) \
+    /*
+     * Pushes a clone of a function with a given [[Prototype]] onto the stack.
+     *   Category: Statements
+     *   Type: Function
+     *   Operands: uint32_t funcIndex
+     *   Stack: proto => obj
+     */ \
+    macro(JSOP_FUNWITHPROTO,   52, "funwithproto",    NULL,         5,  1,  1,  JOF_OBJECT) \
     \
     /*
      * Pops the top of stack value, pushes property of it onto the stack.
diff --git a/js/src/vm/Xdr.h b/js/src/vm/Xdr.h
index 1ca43c63da18..879c899f5ffe 100644
--- a/js/src/vm/Xdr.h
+++ b/js/src/vm/Xdr.h
@@ -29,7 +29,7 @@ namespace js {
  *
  *  https://developer.mozilla.org/en-US/docs/SpiderMonkey/Internals/Bytecode
  */
-static const uint32_t XDR_BYTECODE_VERSION_SUBTRAHEND = 253;
+static const uint32_t XDR_BYTECODE_VERSION_SUBTRAHEND = 254;
 static const uint32_t XDR_BYTECODE_VERSION =
     uint32_t(0xb973c0de - XDR_BYTECODE_VERSION_SUBTRAHEND);