--- a/js/src/jit/IonCode.h
+++ b/js/src/jit/IonCode.h
@@ -593,21 +593,20 @@ struct IonScriptCounts {
 
   void setPrevious(IonScriptCounts* previous) { previous_ = previous; }
 
   IonScriptCounts* previous() const { return previous_; }
 
   size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
     size_t size = 0;
     auto currCounts = this;
-    while (currCounts) {
-      const IonScriptCounts* currCount = currCounts;
-      currCounts = currCount->previous_;
-      size += currCount->sizeOfOneIncludingThis(mallocSizeOf);
-    }
+    do {
+      size += currCounts->sizeOfOneIncludingThis(mallocSizeOf);
+      currCounts = currCounts->previous_;
+    } while (currCounts);
     return size;
   }
 
   size_t sizeOfOneIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
     size_t size = mallocSizeOf(this) + mallocSizeOf(blocks_);
     for (size_t i = 0; i < numBlocks_; i++) {
       blocks_[i].sizeOfExcludingThis(mallocSizeOf);
     }

--- a/js/src/vm/JSScript.cpp
+++ b/js/src/vm/JSScript.cpp
@@ -1494,19 +1494,23 @@ js::PCCounts* ScriptCounts::getThrowCoun
       std::lower_bound(throwCounts_.begin(), throwCounts_.end(), searched);
   if (elem == throwCounts_.end() || elem->pcOffset() != offset) {
     elem = throwCounts_.insert(elem, searched);
   }
   return elem;
 }
 
 size_t ScriptCounts::sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) {
-  return mallocSizeOf(this) + pcCounts_.sizeOfExcludingThis(mallocSizeOf) +
-         throwCounts_.sizeOfExcludingThis(mallocSizeOf) +
-         ionCounts_->sizeOfIncludingThis(mallocSizeOf);
+  size_t size = mallocSizeOf(this);
+  size += pcCounts_.sizeOfExcludingThis(mallocSizeOf);
+  size += throwCounts_.sizeOfExcludingThis(mallocSizeOf);
+  if (ionCounts_) {
+    size += ionCounts_->sizeOfIncludingThis(mallocSizeOf);
+  }
+  return size;
 }
 
 js::PCCounts* JSScript::maybeGetPCCounts(jsbytecode* pc) {
   MOZ_ASSERT(containsPC(pc));
   return getScriptCounts().maybeGetPCCounts(pcToOffset(pc));
 }
 
 const js::PCCounts* JSScript::maybeGetThrowCounts(jsbytecode* pc) {