diff --git a/include/array_view.h b/include/array_view.h
index 006f18c..e4ffe5d 100644
--- a/include/array_view.h
+++ b/include/array_view.h
@@ -75,6 +75,7 @@ namespace details
 	class coordinate_facade
 	{
 		static_assert(std::is_integral<ValueType>::value
+            && !std::is_signed<ValueType>::value
 			&& sizeof(ValueType) <= sizeof(size_t), "ValueType must be unsigned integral type!");
 		static_assert(Rank > 0, "Rank must be greater than 0!");
 
@@ -1629,6 +1630,10 @@ namespace details
 template <typename ValueType, typename SizeType>
 struct array_view_options
 {
+    static_assert(std::is_integral<SizeType>::value
+                  && !std::is_signed<SizeType>::value
+                  && sizeof(SizeType) <= sizeof(size_t), "size_type must be unsigned integral type!");
+
 	struct array_view_traits
 	{
 		using value_type = ValueType;
diff --git a/tests/array_view_tests.cpp b/tests/array_view_tests.cpp
index ba251e8..df25852 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
 		{
@@ -1569,7 +1569,7 @@ SUITE(array_view_tests)
 
 			CHECK(av1 == av2);
 
-			array_view<array_view_options<int, char>, 20> av3 = av1.as_array_view(dim<>(20));
+			array_view<array_view_options<int, unsigned char>, 20> av3 = av1.as_array_view(dim<>(20));
 			CHECK(av3 == av2 && av3 == av1);
 		}