--- a/js/src/jit/BaselineFrame.cpp
+++ b/js/src/jit/BaselineFrame.cpp
@@ -56,20 +56,19 @@ BaselineFrame::trace(JSTracer *trc, JitF
 
     // Mark locals and stack values.
     JSScript *script = this->script();
     size_t nfixed = script->nfixed();
     size_t nlivefixed = script->nbodyfixed();
 
     if (nfixed != nlivefixed) {
         jsbytecode *pc;
-        NestedScopeObject *staticScope;
+        frameIterator.baselineScriptAndPc(nullptr, &pc);
 
-        frameIterator.baselineScriptAndPc(nullptr, &pc);
-        staticScope = script->getStaticScope(pc);
+        NestedScopeObject *staticScope = script->getStaticScope(pc);
         while (staticScope && !staticScope->is<StaticBlockObject>())
             staticScope = staticScope->enclosingNestedScope();
 
         if (staticScope) {
             StaticBlockObject &blockObj = staticScope->as<StaticBlockObject>();
             nlivefixed = blockObj.localOffset() + blockObj.numVariables();
         }
     }

--- a/js/src/vm/Stack.cpp
+++ b/js/src/vm/Stack.cpp
@@ -338,31 +338,33 @@ InterpreterFrame::markValues(JSTracer *t
         gc::MarkValueRootRange(trc, end - start, slots() + start, "vm_stack");
 }
 
 void
 InterpreterFrame::markValues(JSTracer *trc, Value *sp, jsbytecode *pc)
 {
     MOZ_ASSERT(sp >= slots());
 
-    NestedScopeObject *staticScope;
+    JSScript *script = this->script();
+    size_t nfixed = script->nfixed();
+    size_t nlivefixed = script->nbodyfixed();
 
-    staticScope = script()->getStaticScope(pc);
-    while (staticScope && !staticScope->is<StaticBlockObject>())
-        staticScope = staticScope->enclosingNestedScope();
+    if (nfixed != nlivefixed) {
+        NestedScopeObject *staticScope = script->getStaticScope(pc);
+        while (staticScope && !staticScope->is<StaticBlockObject>())
+            staticScope = staticScope->enclosingNestedScope();
 
-    size_t nfixed = script()->nfixed();
-    size_t nlivefixed;
+        if (staticScope) {
+            StaticBlockObject &blockObj = staticScope->as<StaticBlockObject>();
+            nlivefixed = blockObj.localOffset() + blockObj.numVariables();
+        }
+    }
 
-    if (staticScope) {
-        StaticBlockObject &blockObj = staticScope->as<StaticBlockObject>();
-        nlivefixed = blockObj.localOffset() + blockObj.numVariables();
-    } else {
-        nlivefixed = script()->nbodyfixed();
-    }
+    MOZ_ASSERT(nlivefixed <= nfixed);
+    MOZ_ASSERT(nlivefixed >= script->nbodyfixed());
 
     if (nfixed == nlivefixed) {
         // All locals are live.
         markValues(trc, 0, sp - slots());
     } else {
         // Mark operand stack.
         markValues(trc, nfixed, sp - slots());