diff --git a/test_conformance/basic/test_vector_swizzle.cpp b/test_conformance/basic/test_vector_swizzle.cpp
index fdbc891967..6abc19bf7e 100644
--- a/test_conformance/basic/test_vector_swizzle.cpp
+++ b/test_conformance/basic/test_vector_swizzle.cpp
@@ -511,7 +511,7 @@ static void makeReference(std::vector<T>& ref)
     ref.resize(refSize);
     std::fill(ref.begin(), ref.end(), 99);
 
-    size_t dstIndex = 0;
+    volatile size_t dstIndex = 0;
 
     // single channel lvalue
     for (size_t i = 0; i < N; i++)