diff --git a/js/src/ion/CodeGenerator.cpp b/js/src/ion/CodeGenerator.cpp
index 393a1324eb4..b5c2bda7e8c 100644
--- a/js/src/ion/CodeGenerator.cpp
+++ b/js/src/ion/CodeGenerator.cpp
@@ -1423,9 +1423,9 @@ CodeGenerator::visitCallDOMNative(LCallDOMNative *call)
     // Now compute the argv value.  Since StackPointer is pointing to &vp[0] and
     // argv is &vp[2] we just need to add 2*sizeof(Value) to the current
     // StackPointer.
-    JS_STATIC_ASSERT(JSJitMethodCallArgs::offsetOfArgv() == 0);
-    JS_STATIC_ASSERT(JSJitMethodCallArgs::offsetOfArgc() ==
-                     IonDOMMethodExitFrameLayout::offsetOfArgcFromArgv());
+    JS_STATIC_ASSERT(JSJitMethodCallArgsTraits::offsetOfArgv == 0);
+    JS_STATIC_ASSERT(JSJitMethodCallArgsTraits::offsetOfArgc ==
+                     IonDOMMethodExitFrameLayoutTraits::offsetOfArgcFromArgv);
     masm.computeEffectiveAddress(Address(StackPointer, 2 * sizeof(Value)), argArgs);
 
     // GetReservedSlot(obj, DOM_OBJECT_SLOT).toPrivate()
diff --git a/js/src/ion/arm/IonFrames-arm.h b/js/src/ion/arm/IonFrames-arm.h
index 016f0b2650c..f4d337c6171 100644
--- a/js/src/ion/arm/IonFrames-arm.h
+++ b/js/src/ion/arm/IonFrames-arm.h
@@ -462,6 +462,8 @@ class IonDOMExitFrameLayout
     }
 };
 
+struct IonDOMMethodExitFrameLayoutTraits;
+
 class IonDOMMethodExitFrameLayout
 {
     IonExitFooterFrame footer_;
@@ -477,6 +479,8 @@ class IonDOMMethodExitFrameLayout
     uint32_t loCalleeResult_;
     uint32_t hiCalleeResult_;
 
+    friend struct IonDOMMethodExitFrameLayoutTraits;
+
   public:
     static inline size_t Size() {
         return sizeof(IonDOMMethodExitFrameLayout);
@@ -485,10 +489,7 @@ class IonDOMMethodExitFrameLayout
     static size_t offsetOfResult() {
         return offsetof(IonDOMMethodExitFrameLayout, loCalleeResult_);
     }
-    static size_t offsetOfArgcFromArgv() {
-        return offsetof(IonDOMMethodExitFrameLayout, argc_) -
-            offsetof(IonDOMMethodExitFrameLayout, argv_);
-    }
+
     inline Value *vp() {
         // The code in visitCallDOMNative depends on this static assert holding
         JS_STATIC_ASSERT(offsetof(IonDOMMethodExitFrameLayout, loCalleeResult_) ==
@@ -503,6 +504,12 @@ class IonDOMMethodExitFrameLayout
     }
 };
 
+struct IonDOMMethodExitFrameLayoutTraits {
+    static const size_t offsetOfArgcFromArgv =
+        offsetof(IonDOMMethodExitFrameLayout, argc_) -
+        offsetof(IonDOMMethodExitFrameLayout, argv_);
+};
+
 // An invalidation bailout stack is at the stack pointer for the callee frame.
 class InvalidationBailoutStack
 {
diff --git a/js/src/ion/shared/IonFrames-x86-shared.h b/js/src/ion/shared/IonFrames-x86-shared.h
index cb29bef2def..5a22d1cfcef 100644
--- a/js/src/ion/shared/IonFrames-x86-shared.h
+++ b/js/src/ion/shared/IonFrames-x86-shared.h
@@ -427,6 +427,8 @@ class IonDOMExitFrameLayout
     }
 };
 
+struct IonDOMMethodExitFrameLayoutTraits;
+
 class IonDOMMethodExitFrameLayout
 {
   protected: // only to silence a clang warning about unused private fields
@@ -443,6 +445,8 @@ class IonDOMMethodExitFrameLayout
     uint32_t loCalleeResult_;
     uint32_t hiCalleeResult_;
 
+    friend struct IonDOMMethodExitFrameLayoutTraits;
+
   public:
     static inline size_t Size() {
         return sizeof(IonDOMMethodExitFrameLayout);
@@ -451,10 +455,6 @@ class IonDOMMethodExitFrameLayout
     static size_t offsetOfResult() {
         return offsetof(IonDOMMethodExitFrameLayout, loCalleeResult_);
     }
-    static size_t offsetOfArgcFromArgv() {
-        return offsetof(IonDOMMethodExitFrameLayout, argc_) -
-            offsetof(IonDOMMethodExitFrameLayout, argv_);
-    }
 
     inline Value *vp() {
         JS_STATIC_ASSERT(offsetof(IonDOMMethodExitFrameLayout, loCalleeResult_) ==
@@ -469,6 +469,12 @@ class IonDOMMethodExitFrameLayout
     }
 };
 
+struct IonDOMMethodExitFrameLayoutTraits {
+    static const size_t offsetOfArgcFromArgv =
+        offsetof(IonDOMMethodExitFrameLayout, argc_) -
+        offsetof(IonDOMMethodExitFrameLayout, argv_);
+};
+
 class IonOsrFrameLayout : public IonJSFrameLayout
 {
   public:
diff --git a/js/src/jsfriendapi.h b/js/src/jsfriendapi.h
index a61993189c6..420c7a9ddc5 100644
--- a/js/src/jsfriendapi.h
+++ b/js/src/jsfriendapi.h
@@ -1480,6 +1480,8 @@ class JSJitSetterCallArgs : protected JS::MutableHandleValue
     // Add get() or maybe hasDefined() as needed
 };
 
+struct JSJitMethodCallArgsTraits;
+
 /*
  * A class, expected to be passed by reference, which represents the CallArgs
  * for a JSJitMethodOp.
@@ -1488,6 +1490,7 @@ class JSJitMethodCallArgs : protected JS::detail::CallArgsBase<JS::detail::NoUse
 {
   private:
     typedef JS::detail::CallArgsBase<JS::detail::NoUsedRval> Base;
+    friend struct JSJitMethodCallArgsTraits;
 
   public:
     explicit JSJitMethodCallArgs(const JS::CallArgs& args) {
@@ -1509,17 +1512,15 @@ class JSJitMethodCallArgs : protected JS::detail::CallArgsBase<JS::detail::NoUse
         return Base::hasDefined(i);
     }
 
-    static size_t offsetOfArgv() {
-        return offsetof(JSJitMethodCallArgs, argv_);
-    }
-
-    static size_t offsetOfArgc() {
-        return offsetof(JSJitMethodCallArgs, argc_);
-    }
-
     // Add get() as needed
 };
 
+struct JSJitMethodCallArgsTraits
+{
+    static const size_t offsetOfArgv = offsetof(JSJitMethodCallArgs, argv_);
+    static const size_t offsetOfArgc = offsetof(JSJitMethodCallArgs, argc_);
+};
+
 /*
  * This struct contains metadata passed from the DOM to the JS Engine for JIT
  * optimizations on DOM property accessors. Eventually, this should be made