--- a/js/src/vm/Stack.cpp
+++ b/js/src/vm/Stack.cpp
@@ -621,60 +621,58 @@ FrameIter::settleOnActivation()
 
         JS_ASSERT(!data_.interpFrames_.frame()->runningInJit());
         data_.pc_ = data_.interpFrames_.pc();
         data_.state_ = INTERP;
         return;
     }
 }
 
-FrameIter::Data::Data(JSContext *cx, PerThreadData *perThread, SavedOption savedOption,
-                      ContextOption contextOption, JSPrincipals *principals)
-  : perThread_(perThread),
-    cx_(cx),
+FrameIter::Data::Data(JSContext *cx, SavedOption savedOption, ContextOption contextOption,
+                      JSPrincipals *principals)
+  : cx_(cx),
     savedOption_(savedOption),
     contextOption_(contextOption),
     principals_(principals),
     pc_(nullptr),
     interpFrames_(nullptr),
     activations_(cx->runtime())
 #ifdef JS_ION
   , ionFrames_((uint8_t *)nullptr, SequentialExecution)
 #endif
 {
 }
 
 FrameIter::Data::Data(const FrameIter::Data &other)
-  : perThread_(other.perThread_),
-    cx_(other.cx_),
+  : cx_(other.cx_),
     savedOption_(other.savedOption_),
     contextOption_(other.contextOption_),
     principals_(other.principals_),
     state_(other.state_),
     pc_(other.pc_),
     interpFrames_(other.interpFrames_),
     activations_(other.activations_)
 #ifdef JS_ION
   , ionFrames_(other.ionFrames_)
 #endif
 {
 }
 
 FrameIter::FrameIter(JSContext *cx, SavedOption savedOption)
-  : data_(cx, &cx->runtime()->mainThread, savedOption, CURRENT_CONTEXT, nullptr)
+  : data_(cx, savedOption, CURRENT_CONTEXT, nullptr)
 #ifdef JS_ION
     , ionInlineFrames_(cx, (js::jit::IonFrameIterator*) nullptr)
 #endif
 {
     settleOnActivation();
 }
 
 FrameIter::FrameIter(JSContext *cx, ContextOption contextOption,
                      SavedOption savedOption, JSPrincipals *principals)
-  : data_(cx, &cx->runtime()->mainThread, savedOption, contextOption, principals)
+  : data_(cx, savedOption, contextOption, principals)
 #ifdef JS_ION
     , ionInlineFrames_(cx, (js::jit::IonFrameIterator*) nullptr)
 #endif
 {
     settleOnActivation();
 }
 
 FrameIter::FrameIter(const FrameIter &other)

--- a/js/src/vm/Stack.h
+++ b/js/src/vm/Stack.h
@@ -1484,35 +1484,34 @@ class FrameIter
     enum SavedOption { STOP_AT_SAVED, GO_THROUGH_SAVED };
     enum ContextOption { CURRENT_CONTEXT, ALL_CONTEXTS };
     enum State { DONE, INTERP, JIT, ASMJS };
 
     // Unlike ScriptFrameIter itself, ScriptFrameIter::Data can be allocated on
     // the heap, so this structure should not contain any GC things.
     struct Data
     {
-        PerThreadData * perThread_;
         JSContext *     cx_;
         SavedOption     savedOption_;
         ContextOption   contextOption_;
         JSPrincipals *  principals_;
 
         State           state_;
 
         jsbytecode *    pc_;
 
         InterpreterFrameIterator interpFrames_;
         ActivationIterator activations_;
 
 #ifdef JS_ION
         jit::IonFrameIterator ionFrames_;
 #endif
 
-        Data(JSContext *cx, PerThreadData *perThread, SavedOption savedOption,
-             ContextOption contextOption, JSPrincipals *principals);
+        Data(JSContext *cx, SavedOption savedOption, ContextOption contextOption,
+             JSPrincipals *principals);
         Data(const Data &other);
     };
 
     FrameIter(JSContext *cx, SavedOption = STOP_AT_SAVED);
     FrameIter(JSContext *cx, ContextOption, SavedOption, JSPrincipals* = nullptr);
     FrameIter(const FrameIter &iter);
     FrameIter(const Data &data);
     FrameIter(AbstractFramePtr frame);