diff --git a/SPIRV/GlslangToSpv.h b/SPIRV/GlslangToSpv.h
index 11e22f58..aba48a38 100644
--- a/SPIRV/GlslangToSpv.h
+++ b/SPIRV/GlslangToSpv.h
@@ -32,6 +32,8 @@
 // ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 // POSSIBILITY OF SUCH DAMAGE.
 
+#pragma once
+
 #if _MSC_VER >= 1900
     #pragma warning(disable : 4464) // relative include path contains '..'
 #endif
diff --git a/SPIRV/doc.h b/SPIRV/doc.h
index 7dcc51dd..710ca1a5 100644
--- a/SPIRV/doc.h
+++ b/SPIRV/doc.h
@@ -36,6 +36,8 @@
 // Parameterize the SPIR-V enumerants.
 //
 
+#pragma once
+
 #include "spirv.hpp"
 
 #include <vector>
diff --git a/StandAlone/StandAlone.cpp b/StandAlone/StandAlone.cpp
index b21f20d4..d713e760 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/LiveTraverser.h b/glslang/MachineIndependent/LiveTraverser.h
index 029c24a8..7333bc96 100644
--- a/glslang/MachineIndependent/LiveTraverser.h
+++ b/glslang/MachineIndependent/LiveTraverser.h
@@ -33,6 +33,8 @@
 // POSSIBILITY OF SUCH DAMAGE.
 //
 
+#pragma once
+
 #include "../Include/Common.h"
 #include "reflection.h"
 #include "localintermediate.h"
diff --git a/glslang/MachineIndependent/RemoveTree.h b/glslang/MachineIndependent/RemoveTree.h
index 507307e4..1ed01562 100644
--- a/glslang/MachineIndependent/RemoveTree.h
+++ b/glslang/MachineIndependent/RemoveTree.h
@@ -32,6 +32,8 @@
 // POSSIBILITY OF SUCH DAMAGE.
 //
 
+#pragma once
+
 namespace glslang {
 
 void RemoveAllTreeNodes(TIntermNode*);
diff --git a/glslang/MachineIndependent/ScanContext.h b/glslang/MachineIndependent/ScanContext.h
index 1d86348e..608ae067 100644
--- a/glslang/MachineIndependent/ScanContext.h
+++ b/glslang/MachineIndependent/ScanContext.h
@@ -38,6 +38,8 @@
 // sits between the preprocessor scanner and parser.
 //
 
+#pragma once
+
 #include "ParseHelper.h"
 
 namespace glslang {
diff --git a/glslang/MachineIndependent/gl_types.h b/glslang/MachineIndependent/gl_types.h
index d7cb31fe..ae00ae57 100644
--- a/glslang/MachineIndependent/gl_types.h
+++ b/glslang/MachineIndependent/gl_types.h
@@ -21,6 +21,8 @@
 ** MATERIALS OR THE USE OR OTHER DEALINGS IN THE MATERIALS.
 */
 
+#pragma once
+
 #define GL_FLOAT                          0x1406
 #define GL_FLOAT_VEC2                     0x8B50
 #define GL_FLOAT_VEC3                     0x8B51
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
 
diff --git a/glslang/MachineIndependent/propagateNoContraction.h b/glslang/MachineIndependent/propagateNoContraction.h
index 3412c85d..8521ad7d 100644
--- a/glslang/MachineIndependent/propagateNoContraction.h
+++ b/glslang/MachineIndependent/propagateNoContraction.h
@@ -37,6 +37,8 @@
 // propagate 'noContraction' qualifier.
 //
 
+#pragma once
+
 #include "../Include/intermediate.h"
 
 namespace glslang {