diff --git a/src/physfs_internal.h b/src/physfs_internal.h
index 8b221ab..07677c7 100644
--- a/src/physfs_internal.h
+++ b/src/physfs_internal.h
@@ -15,7 +15,7 @@
 #endif
 
 /* Turn off MSVC warnings that are aggressively anti-portability. */
-#ifdef _MSC_VER
+#if defined(_MSC_VER) && !defined(_CRT_SECURE_NO_WARNINGS)
 #define _CRT_SECURE_NO_WARNINGS 1
 #endif
 
diff --git a/src/physfs_platform_windows.c b/src/physfs_platform_windows.c
index 49d6f55..1a40302 100644
--- a/src/physfs_platform_windows.c
+++ b/src/physfs_platform_windows.c
@@ -16,6 +16,10 @@
 #undef UNICODE
 #endif
 
+#if defined(_MSC_VER) && !defined(_CRT_SECURE_NO_WARNINGS)
+#define _CRT_SECURE_NO_WARNINGS 1
+#endif
+
 #define WIN32_LEAN_AND_MEAN 1
 #include <windows.h>
 
diff --git a/src/physfs_platform_winrt.cpp b/src/physfs_platform_winrt.cpp
index 5acc8c4..f50fc9d 100644
--- a/src/physfs_platform_winrt.cpp
+++ b/src/physfs_platform_winrt.cpp
@@ -17,6 +17,9 @@
 
 #ifdef PHYSFS_PLATFORM_WINRT
 
+#if defined(_MSC_VER) && !defined(_CRT_SECURE_NO_WARNINGS)
+#define _CRT_SECURE_NO_WARNINGS 1
+#endif
 #include <windows.h>
 
 #include "physfs_internal.h"