diff --git a/src/sfizz/Voice.h b/src/sfizz/Voice.h
index 6967e780..45802d2f 100644
--- a/src/sfizz/Voice.h
+++ b/src/sfizz/Voice.h
@@ -392,9 +392,11 @@ private:
     template <class F>
     void forEachWithSmoother(sfz::Mod modId, F&& lambda)
     {
+        size_t count = region->modifiers[modId].size();
+        ASSERT(count == modifierSmoothers[modId].size());
         auto mod = region->modifiers[modId].begin();
         auto smoother = modifierSmoothers[modId].begin();
-        while (mod < region->modifiers[modId].end()) {
+        for (size_t i = 0; i < count; ++i) {
             lambda(*mod, *smoother);
             incrementAll(mod, smoother);
         }