diff --git a/StandAlone/StandAlone.cpp b/StandAlone/StandAlone.cpp
index 3faadecf..76af8fe3 100644
--- a/StandAlone/StandAlone.cpp
+++ b/StandAlone/StandAlone.cpp
@@ -35,7 +35,9 @@
 //
 
 // this only applies to the standalone wrapper, not the front end in general
+#ifndef _CRT_SECURE_NO_WARNINGS
 #define _CRT_SECURE_NO_WARNINGS
+#endif
 
 #include "ResourceLimits.h"
 #include "Worklist.h"
diff --git a/glslang/MachineIndependent/preprocessor/Pp.cpp b/glslang/MachineIndependent/preprocessor/Pp.cpp
index e71e79c4..293ada6c 100644
--- a/glslang/MachineIndependent/preprocessor/Pp.cpp
+++ b/glslang/MachineIndependent/preprocessor/Pp.cpp
@@ -76,7 +76,9 @@ TORT (INCLUDING NEGLIGENCE), STRICT LIABILITY OR OTHERWISE, EVEN IF
 NVIDIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 \****************************************************************************/
 
+#ifndef _CRT_SECURE_NO_WARNINGS
 #define _CRT_SECURE_NO_WARNINGS
+#endif
 
 #include <sstream>
 #include <cstdlib>
diff --git a/glslang/MachineIndependent/preprocessor/PpAtom.cpp b/glslang/MachineIndependent/preprocessor/PpAtom.cpp
index 52df3b02..06c2333e 100644
--- a/glslang/MachineIndependent/preprocessor/PpAtom.cpp
+++ b/glslang/MachineIndependent/preprocessor/PpAtom.cpp
@@ -76,7 +76,9 @@ TORT (INCLUDING NEGLIGENCE), STRICT LIABILITY OR OTHERWISE, EVEN IF
 NVIDIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 \****************************************************************************/
 
+#ifndef _CRT_SECURE_NO_WARNINGS
 #define _CRT_SECURE_NO_WARNINGS
+#endif
 
 #include <cassert>
 #include <cstdlib>
diff --git a/glslang/MachineIndependent/preprocessor/PpScanner.cpp b/glslang/MachineIndependent/preprocessor/PpScanner.cpp
index e72efc04..cee45ce7 100644
--- a/glslang/MachineIndependent/preprocessor/PpScanner.cpp
+++ b/glslang/MachineIndependent/preprocessor/PpScanner.cpp
@@ -76,7 +76,9 @@ TORT (INCLUDING NEGLIGENCE), STRICT LIABILITY OR OTHERWISE, EVEN IF
 NVIDIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 \****************************************************************************/
 
+#ifndef _CRT_SECURE_NO_WARNINGS
 #define _CRT_SECURE_NO_WARNINGS
+#endif
 
 #include <cstdlib>
 #include <cstring>
diff --git a/glslang/MachineIndependent/preprocessor/PpTokens.cpp b/glslang/MachineIndependent/preprocessor/PpTokens.cpp
index 7fa06a5a..4baf99e0 100644
--- a/glslang/MachineIndependent/preprocessor/PpTokens.cpp
+++ b/glslang/MachineIndependent/preprocessor/PpTokens.cpp
@@ -80,8 +80,10 @@ NVIDIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 // For recording and playing back the stream of tokens in a macro definition.
 //
 
-#if (defined(_MSC_VER) && _MSC_VER < 1900 /*vs2015*/)
+#ifndef _CRT_SECURE_NO_WARNINGS
 #define _CRT_SECURE_NO_WARNINGS
+#endif
+#if (defined(_MSC_VER) && _MSC_VER < 1900 /*vs2015*/)
 #define snprintf sprintf_s
 #endif