diff --git a/include/array_view.h b/include/array_view.h
index 006f18c..d14a548 100644
--- a/include/array_view.h
+++ b/include/array_view.h
@@ -75,7 +75,7 @@ namespace details
 	class coordinate_facade
 	{
 		static_assert(std::is_integral<ValueType>::value
-			&& sizeof(ValueType) <= sizeof(size_t), "ValueType must be unsigned integral type!");
+			&& std::is_unsigned<ValueType>::value, "ValueType must be unsigned integral type!");
 		static_assert(Rank > 0, "Rank must be greater than 0!");
 
 		template <typename OtherConcreteType, typename OtherValueType, unsigned int OtherRank>
@@ -771,7 +771,7 @@ class static_bounds<SizeType, FirstRange, RestRanges...>
 {
 	using MyRanges = details::BoundsRanges <SizeType, FirstRange, RestRanges... >;
 	static_assert(std::is_integral<SizeType>::value
-		&& details::SizeTypeTraits<SizeType>::max_value <= SIZE_MAX, "SizeType must be an integral type and its numeric limits must be smaller than SIZE_MAX");
+		&& details::SizeTypeTraits<SizeType>::max_value <= (std::numeric_limits<size_t>::max)(), "SizeType must be an integral type and its numeric limits must be smaller than max size_t.");
 
 	MyRanges m_ranges;
 	_CONSTEXPR static_bounds(const MyRanges & range) : m_ranges(range) { }
diff --git a/tests/array_view_tests.cpp b/tests/array_view_tests.cpp
index ba251e8..8a4376c 100644
--- a/tests/array_view_tests.cpp
+++ b/tests/array_view_tests.cpp
@@ -1305,7 +1305,7 @@ SUITE(array_view_tests)
 	TEST(custmized_array_view_size)
 	{
 		double (*arr)[3][4] = new double[100][3][4];
-		array_view<array_view_options<double, char>, dynamic_range, 3, 4> av1(arr, (char)10);
+		array_view<array_view_options<double, unsigned char>, dynamic_range, 3, 4> av1(arr, (char)10);
 
 		struct EffectiveStructure
 		{