diff --git a/js/src/wasm/WasmTypes.h b/js/src/wasm/WasmTypes.h
index 167b04365d56..7383a4addc15 100644
--- a/js/src/wasm/WasmTypes.h
+++ b/js/src/wasm/WasmTypes.h
@@ -1846,10 +1846,13 @@ class DebugFrame
         void* flagsWord_;
     };
 
+    // Avoid -Wunused-private-field warnings.
+  protected:
 #if JS_BITS_PER_WORD == 32
     uint32_t padding_;  // See alignmentStaticAsserts().
 #endif
 
+  private:
     // The Frame goes at the end since the stack grows down.
     Frame frame_;