diff --git a/Utilities/WaveFrontReader.h b/Utilities/WaveFrontReader.h
index c46412b..26e29d7 100644
--- a/Utilities/WaveFrontReader.h
+++ b/Utilities/WaveFrontReader.h
@@ -78,6 +78,9 @@ namespace DX
         {
             Clear();
 
+            if (!szFileName)
+                return E_INVALIDARG;
+
             constexpr size_t MAX_POLY = 64;
 
             using namespace DirectX;
@@ -421,6 +424,9 @@ namespace DX
 
         HRESULT LoadMTL(_In_z_ const wchar_t* szFileName)
         {
+            if (!szFileName)
+                return E_INVALIDARG;
+
             using namespace DirectX;
 
             // Assumes MTL is in CWD along with OBJ
@@ -583,10 +589,13 @@ namespace DX
 
         HRESULT LoadVBO(_In_z_ const wchar_t* szFileName)
         {
-            using namespace DirectX;
-
             Clear();
 
+            if (!szFileName)
+                return E_INVALIDARG;
+
+            using namespace DirectX;
+
     #ifdef _WIN32
             wchar_t fname[_MAX_FNAME] = {};
             _wsplitpath_s(szFileName, nullptr, 0, nullptr, 0, fname, _MAX_FNAME, nullptr, 0);