diff --git a/tests/validation/reference/Gaussian3x3.cpp b/tests/validation/reference/Gaussian3x3.cpp
index c71eade..5ca24a7 100644
--- a/tests/validation/reference/Gaussian3x3.cpp
+++ b/tests/validation/reference/Gaussian3x3.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017 ARM Limited.
+ * Copyright (c) 2017-2019 ARM Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -39,8 +39,10 @@
 {
     SimpleTensor<T> dst(src.shape(), src.data_type());
     const std::array<T, 9> filter{ { 1, 2, 1, 2, 4, 2, 1, 2, 1 } };
-    const float scale = 1.f / 16.f;
-    for(int element_idx = 0; element_idx < src.num_elements(); ++element_idx)
+    const float    scale        = 1.f / 16.f;
+    const uint32_t num_elements = src.num_elements();
+
+    for(uint32_t element_idx = 0; element_idx < num_elements; ++element_idx)
     {
         const Coordinates id = index2coord(src.shape(), element_idx);
         apply_2d_spatial_filter(id, src, dst, TensorShape(3U, 3U), filter.data(), scale, border_mode, constant_border_value);