diff --git a/src/mpack/mpack-platform.c b/src/mpack/mpack-platform.c
index d9595e6..d552f5c 100644
--- a/src/mpack/mpack-platform.c
+++ b/src/mpack/mpack-platform.c
@@ -67,7 +67,7 @@ void mpack_assert_fail(const char* message) {
 
     #if defined(__GCC__) || defined(__clang__)
     __builtin_trap();
-    #elif WIN32
+    #elif defined(WIN32)
     __debugbreak();
     #endif
 
@@ -89,7 +89,7 @@ void mpack_break_hit(const char* message) {
 
     #if defined(__GCC__) || defined(__clang__)
     __builtin_trap();
-    #elif WIN32
+    #elif defined(WIN32)
     __debugbreak();
     #elif MPACK_STDLIB
     abort();
diff --git a/src/mpack/mpack-platform.h b/src/mpack/mpack-platform.h
index bbcfb60..860c747 100644
--- a/src/mpack/mpack-platform.h
+++ b/src/mpack/mpack-platform.h
@@ -90,7 +90,7 @@ extern "C" {
     #define MPACK_UNREACHABLE __builtin_unreachable()
     #define MPACK_NORETURN(fn) fn __attribute__((noreturn))
     #define MPACK_ALWAYS_INLINE __attribute__((always_inline)) static inline
-#elif _MSC_VER
+#elif defined(_MSC_VER)
     #define MPACK_UNREACHABLE __assume(0)
     #define MPACK_NORETURN(fn) __declspec(noreturn) fn
     #define MPACK_ALWAYS_INLINE __forceinline static