diff --git a/CMakeLists.txt b/CMakeLists.txt
index 103e9a3..a2c260f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -21,6 +21,17 @@ endif()
 message(STATUS "Building in ${CMAKE_BUILD_TYPE} mode")
 message(STATUS "Building with ${CMAKE_C_COMPILER_ID} ${CMAKE_C_COMPILER_VERSION} on ${CMAKE_SYSTEM}")
 
+function(IsMSVC var)
+    if (MSVC OR (CMAKE_C_COMPILER_ID STREQUAL "Clang" AND CMAKE_C_SIMULATE_ID STREQUAL "MSVC"))
+        set(${var} 1 PARENT_SCOPE)
+    else()
+        set(${var} 0 PARENT_SCOPE)
+    endif()
+endfunction()
+
+set(is_msvc 0)
+IsMSVC(is_msvc)
+
 macro(xcheck_add_c_compiler_flag FLAG)
     string(REPLACE "-" "" FLAG_NO_HYPHEN ${FLAG})
     check_c_compiler_flag(${FLAG} COMPILER_SUPPORTS_${FLAG_NO_HYPHEN})
@@ -30,7 +41,7 @@ macro(xcheck_add_c_compiler_flag FLAG)
 endmacro()
 
 xcheck_add_c_compiler_flag(-Wall)
-if(NOT MSVC)
+if(NOT is_msvc)
     xcheck_add_c_compiler_flag(-Werror)
     xcheck_add_c_compiler_flag(-Wextra)
 endif()
@@ -45,7 +56,7 @@ xcheck_add_c_compiler_flag(-Wno-format-truncation)
 xcheck_add_c_compiler_flag(-funsigned-char)
 
 # ClangCL is command line compatible with MSVC, so 'MSVC' is set.
-if(MSVC)
+if(${is_msvc})
     xcheck_add_c_compiler_flag(-Wno-unsafe-buffer-usage)
     xcheck_add_c_compiler_flag(-Wno-sign-conversion)
     xcheck_add_c_compiler_flag(-Wno-nonportable-system-include-path)
@@ -54,7 +65,7 @@ if(MSVC)
     xcheck_add_c_compiler_flag(-Wno-reserved-macro-identifier)
     xcheck_add_c_compiler_flag(-Wno-reserved-identifier)
     xcheck_add_c_compiler_flag(-Wdeprecated-declarations)
-    add_compile_definitions(WIN32_LEAN_AND_MEAN)
+    add_compile_definitions(WIN32_LEAN_AND_MEAN _CRT_SECURE_NO_WARNINGS _CRT_NONSTDC_NO_DEPRECATE)
 endif()
 
 if(CMAKE_BUILD_TYPE MATCHES "Debug")
@@ -146,7 +157,7 @@ if(BUILD_QJS_LIBC)
 endif()
 list(APPEND qjs_defines _GNU_SOURCE)
 list(APPEND qjs_libs qjs ${CMAKE_DL_LIBS})
-if(NOT MSVC)
+if(NOT is_msvc)
     list(APPEND qjs_libs m pthread)
 endif()
 
diff --git a/cutils.c b/cutils.c
index 088e75e..6c9f1c9 100644
--- a/cutils.c
+++ b/cutils.c
@@ -612,6 +612,7 @@ void rqsort(void *base, size_t nmemb, size_t size, cmp_f cmp, void *opaque)
 }
 
 #if defined(_MSC_VER)
+struct timezone;
  // From: https://stackoverflow.com/a/26085827
 static int gettimeofday_msvc(struct timeval *tp, struct timezone *tzp)
 {
diff --git a/quickjs.c b/quickjs.c
index 2ea44cc..1d29ce1 100644
--- a/quickjs.c
+++ b/quickjs.c
@@ -211,8 +211,6 @@ typedef enum {
     JS_GC_PHASE_REMOVE_CYCLES,
 } JSGCPhaseEnum;
 
-typedef enum OPCodeEnum OPCodeEnum;
-
 struct JSRuntime {
     JSMallocFunctions mf;
     JSMallocState malloc_state;
@@ -977,7 +975,7 @@ typedef enum OPCodeFormat {
 #undef FMT
 } OPCodeFormat;
 
-enum OPCodeEnum {
+typedef enum OPCodeEnum {
 #define FMT(f)
 #define DEF(id, size, n_pop, n_push, f) OP_ ## id,
 #define def(id, size, n_pop, n_push, f)
@@ -997,7 +995,7 @@ enum OPCodeEnum {
 #undef DEF
 #undef FMT
     OP_TEMP_END,
-};
+} OPCodeEnum;
 
 static int JS_InitAtoms(JSRuntime *rt);
 static JSAtom __JS_NewAtomInit(JSRuntime *rt, const char *str, int len,