diff --git a/js/src/jit-test/tests/basic/bug1344315.js b/js/src/jit-test/tests/basic/bug1344315.js
new file mode 100644
index 0000000000000..b67b274f9cdcc
--- /dev/null
+++ b/js/src/jit-test/tests/basic/bug1344315.js
@@ -0,0 +1,3 @@
+if (helperThreadCount() === 0)
+  quit();
+evalInCooperativeThread('cooperativeYield(); var dbg = new Debugger();');
diff --git a/js/src/vm/Runtime.cpp b/js/src/vm/Runtime.cpp
index 9fd4cab8293ef..7f8986aa43bb2 100644
--- a/js/src/vm/Runtime.cpp
+++ b/js/src/vm/Runtime.cpp
@@ -342,6 +342,13 @@ JSRuntime::destroyRuntime()
 static void
 CheckCanChangeActiveContext(JSRuntime* rt)
 {
+    // The runtime might not currently have an active context, in which case
+    // the accesses below to ActiveThreadData data would not normally be
+    // allowed. Suppress protected data checks so these accesses will be
+    // tolerated --- if the active context is null then we're about to set it
+    // to the current thread.
+    AutoNoteSingleThreadedRegion anstr;
+
     MOZ_RELEASE_ASSERT(!rt->activeContextChangeProhibited());
     MOZ_RELEASE_ASSERT(!rt->activeContext() || rt->gc.canChangeActiveContext(rt->activeContext()));
 
diff --git a/js/src/vm/Runtime.h b/js/src/vm/Runtime.h
index 8ce1dfdf0fe5d..a1d6f3901be28 100644
--- a/js/src/vm/Runtime.h
+++ b/js/src/vm/Runtime.h
@@ -340,11 +340,11 @@ struct JSRuntime : public js::MallocProvider<JSRuntime>
     js::ActiveThreadData<js::Vector<js::CooperatingContext, 4, js::SystemAllocPolicy>> cooperatingContexts_;
 
     // Count of AutoProhibitActiveContextChange instances on the active context.
-    mozilla::Atomic<size_t> activeContextChangeProhibited_;
+    js::ActiveThreadData<size_t> activeContextChangeProhibited_;
 
     // Count of beginSingleThreadedExecution() calls that have occurred with no
     // matching endSingleThreadedExecution().
-    mozilla::Atomic<size_t> singleThreadedExecutionRequired_;
+    js::ActiveThreadData<size_t> singleThreadedExecutionRequired_;
 
     // Whether some thread has called beginSingleThreadedExecution() and we are
     // in the associated callback (which may execute JS on other threads).