diff --git a/CMakeLists.txt b/CMakeLists.txt
index a7ebfc1..3e47224 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -92,7 +92,9 @@
 endif(CMAKE_COMPILER_IS_CLANG)
 
 if(MSVC)
-    set(CMAKE_C_FLAGS_CHECK       "/WX")
+    # Strictest warnings, and treat as errors
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /W3")
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /WX")
 endif(MSVC)
 
 if(CMAKE_BUILD_TYPE STREQUAL "Coverage")
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 21583c4..bedf21b 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -39,7 +39,9 @@
 endif(CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_CLANG)
 
 if(MSVC)
-    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /w") # no warnings here
+    # If a warning level has been defined, suppress all warnings for test code
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /W0")
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /WX-")
 endif(MSVC)
 
 add_test_suite(aes aes.ecb)