diff --git a/include/span.h b/include/span.h
index 32cf828..f4a57d9 100644
--- a/include/span.h
+++ b/include/span.h
@@ -55,6 +55,7 @@
 // turn off some misguided warnings
 #pragma warning(push)
 #pragma warning(disable: 4351) // warns about newly introduced aggregate initializer behavior
+#pragma warning(disable: 4512) // warns that assignment op could not be generated
 
 #endif // _MSC_VER <= 1800
 
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 3435a7f..d49cf93 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -14,6 +14,7 @@ add_definitions(-DGSL_THROWS_FOR_TESTING)
 if(MSVC14 OR MSVC12) # has the support we need
     # remove unnecessary warnings about unchecked iterators
     add_definitions(-D_SCL_SECURE_NO_WARNINGS)
+    add_compile_options(/W4)
 else()
     include(CheckCXXCompilerFlag)
     CHECK_CXX_COMPILER_FLAG("-std=c++14" COMPILER_SUPPORTS_CXX14)
diff --git a/tests/span_tests.cpp b/tests/span_tests.cpp
index 4c21116..ae14f20 100644
--- a/tests/span_tests.cpp
+++ b/tests/span_tests.cpp
@@ -198,6 +198,7 @@ SUITE(span_tests)
 
 			string str = "ttttttttttttttt"; // size = 15
 			auto t = str.data();
+            (void)t;
 			auto av3 = as_span(str);
 			overloaded_func(av3.as_span(dim<>(1), dim<3>(), dim<5>()), 't');
 		}
@@ -223,12 +224,12 @@ SUITE(span_tests)
 		}
 	}
 	
-	template <class Bounds> void fn(const Bounds& b) { static_assert(Bounds::static_size == 60, "static bounds is wrong size"); }
+	template <class Bounds> void fn(const Bounds&) { static_assert(Bounds::static_size == 60, "static bounds is wrong size"); }
 	TEST (span_reshape_test)
 	{
 		int a[3][4][5];
 		auto av = as_span(a);
-        	fn(av.bounds());
+    	fn(av.bounds());
 		auto av2 = av.as_span(dim<60>());
 		auto av3 = av2.as_span(dim<3>(), dim<4>(), dim<5>());
 		auto av4 = av3.as_span(dim<4>(), dim<>(3), dim<5>());
@@ -755,6 +756,7 @@ SUITE(span_tests)
 			CHECK_THROW(empty_av.cbegin()[0], fail_fast);		
 			for (auto& v : empty_av)
 			{
+                (void)v;
 				CHECK(false);
 			}
 		}
@@ -767,6 +769,7 @@ SUITE(span_tests)
 			CHECK_THROW(empty_av.cbegin()[0], fail_fast); 
 			for (auto& v : empty_av)
 			{
+                (void)v;
 				CHECK(false);
 			}
 		}
@@ -782,6 +785,7 @@ SUITE(span_tests)
 
 			for (auto& v : empty_sav)
 			{
+                (void)v;
 				CHECK(false);
 			}
 		}
@@ -796,6 +800,7 @@ SUITE(span_tests)
 
 			for (auto& v : empty_sav)
 			{
+                (void)v;
 				CHECK(false);
 			}
 		}
diff --git a/tests/string_span_tests.cpp b/tests/string_span_tests.cpp
index ab48fcb..5d4681a 100644
--- a/tests/string_span_tests.cpp
+++ b/tests/string_span_tests.cpp
@@ -41,14 +41,14 @@ SUITE(string_span_tests)
     {
         std::string s = "Hello there world";
         cstring_span<> v = s;
-        CHECK(v.length() == s.length());
+        CHECK(v.length() == static_cast<cstring_span<>::size_type>(s.length()));
     }
 
     TEST(TestConstructFromStdVector)
     {
         std::vector<char> vec(5, 'h');
         string_span<> v = vec;
-        CHECK(v.length() == vec.size());
+        CHECK(v.length() == static_cast<string_span<>::size_type>(vec.size()));
     }
 
 	TEST(TestStackArrayConstruction)
@@ -114,7 +114,7 @@ SUITE(string_span_tests)
         char stack_string[] = "Hello";
         cstring_span<> v = ensure_z(stack_string);
         auto s2 = gsl::to_string(v);
-        CHECK(s2.length() == v.length());
+        CHECK(static_cast<cstring_span<>::size_type>(s2.length()) == v.length());
         CHECK(s2.length() == 5);
     }
 }