diff --git a/doomclassic/doom/d_main.cpp b/doomclassic/doom/d_main.cpp
index dce8f1a47..f6bb128b2 100644
--- a/doomclassic/doom/d_main.cpp
+++ b/doomclassic/doom/d_main.cpp
@@ -845,9 +845,9 @@ bool D_DoomMainPoll(void)
 	if (p && p < ::g->myargc-1)
 	{
 		if (M_CheckParm("-cdrom"))
-			sprintf(file, "c:\\doomdata\\"SAVEGAMENAME"%c.dsg",::g->myargv[p+1][0]);
+			sprintf(file, "c:\\doomdata\\" SAVEGAMENAME "%c.dsg",::g->myargv[p+1][0]);
 		else
-			sprintf(file, SAVEGAMENAME"%c.dsg",::g->myargv[p+1][0]);
+			sprintf(file, SAVEGAMENAME "%c.dsg",::g->myargv[p+1][0]);
 		G_LoadGame (file);
 	}
 
diff --git a/doomclassic/doomclassic.vcxproj b/doomclassic/doomclassic.vcxproj
index e3f1304f3..a42c343cb 100644
--- a/doomclassic/doomclassic.vcxproj
+++ b/doomclassic/doomclassic.vcxproj
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+<Project DefaultTargets="Build" ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup Label="ProjectConfigurations">
     <ProjectConfiguration Include="Debug|Win32">
       <Configuration>Debug</Configuration>
@@ -159,18 +159,21 @@
     </SccLocalPath>
     <SccProvider>
     </SccProvider>
+    <WindowsTargetPlatformVersion>10.0.17763.0</WindowsTargetPlatformVersion>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
     <ConfigurationType>StaticLibrary</ConfigurationType>
     <UseDebugLibraries>true</UseDebugLibraries>
     <CharacterSet>Unicode</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">
     <ConfigurationType>StaticLibrary</ConfigurationType>
     <UseDebugLibraries>false</UseDebugLibraries>
     <WholeProgramOptimization>true</WholeProgramOptimization>
     <CharacterSet>Unicode</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
   <ImportGroup Label="ExtensionSettings">
diff --git a/doomclassic/timidity/timidity.vcxproj b/doomclassic/timidity/timidity.vcxproj
index 76f1ca7d0..1d2fcd95f 100644
--- a/doomclassic/timidity/timidity.vcxproj
+++ b/doomclassic/timidity/timidity.vcxproj
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+<Project DefaultTargets="Build" ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup Label="ProjectConfigurations">
     <ProjectConfiguration Include="Debug|Win32">
       <Configuration>Debug</Configuration>
@@ -52,18 +52,21 @@
     </SccLocalPath>
     <SccProvider>
     </SccProvider>
+    <WindowsTargetPlatformVersion>10.0.17763.0</WindowsTargetPlatformVersion>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
     <ConfigurationType>StaticLibrary</ConfigurationType>
     <UseDebugLibraries>true</UseDebugLibraries>
     <CharacterSet>Unicode</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">
     <ConfigurationType>StaticLibrary</ConfigurationType>
     <UseDebugLibraries>false</UseDebugLibraries>
     <WholeProgramOptimization>true</WholeProgramOptimization>
     <CharacterSet>Unicode</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
   <ImportGroup Label="ExtensionSettings">
diff --git a/neo/amplitude/amplitude.vcxproj b/neo/amplitude/amplitude.vcxproj
index b16f24b79..adab6b842 100644
--- a/neo/amplitude/amplitude.vcxproj
+++ b/neo/amplitude/amplitude.vcxproj
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+<Project DefaultTargets="Build" ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup Label="ProjectConfigurations">
     <ProjectConfiguration Include="Debug|Win32">
       <Configuration>Debug</Configuration>
@@ -29,24 +29,28 @@
     </SccLocalPath>
     <SccProvider>
     </SccProvider>
+    <WindowsTargetPlatformVersion>10.0.17763.0</WindowsTargetPlatformVersion>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
     <ConfigurationType>Application</ConfigurationType>
     <UseDebugLibraries>true</UseDebugLibraries>
     <CharacterSet>Unicode</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">
     <ConfigurationType>Application</ConfigurationType>
     <UseDebugLibraries>false</UseDebugLibraries>
     <WholeProgramOptimization>true</WholeProgramOptimization>
     <CharacterSet>Unicode</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Retail|Win32'" Label="Configuration">
     <ConfigurationType>Application</ConfigurationType>
     <UseDebugLibraries>false</UseDebugLibraries>
     <WholeProgramOptimization>true</WholeProgramOptimization>
     <CharacterSet>Unicode</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
   <ImportGroup Label="ExtensionSettings">
diff --git a/neo/d3xp/gamesys/SysCmds.cpp b/neo/d3xp/gamesys/SysCmds.cpp
index a8f2f86ed..7236cc3f8 100644
--- a/neo/d3xp/gamesys/SysCmds.cpp
+++ b/neo/d3xp/gamesys/SysCmds.cpp
@@ -130,7 +130,7 @@ void Cmd_ListSpawnArgs_f( const idCmdArgs &args ) {
 
 	for ( i = 0; i < ent->spawnArgs.GetNumKeyVals(); i++ ) {
 		const idKeyValue *kv = ent->spawnArgs.GetKeyVal( i );
-		gameLocal.Printf( "\"%s\"  "S_COLOR_WHITE"\"%s\"\n", kv->GetKey().c_str(), kv->GetValue().c_str() );
+		gameLocal.Printf( "\"%s\"  " S_COLOR_WHITE "\"%s\"\n", kv->GetKey().c_str(), kv->GetValue().c_str() );
 	}
 }
 
diff --git a/neo/doomexe.vcxproj b/neo/doomexe.vcxproj
index 6a7bcb4b1..505d85942 100644
--- a/neo/doomexe.vcxproj
+++ b/neo/doomexe.vcxproj
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+<Project DefaultTargets="Build" ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup Label="ProjectConfigurations">
     <ProjectConfiguration Include="Debug|Win32">
       <Configuration>Debug</Configuration>
@@ -27,21 +27,25 @@
     <Keyword>Win32Proj</Keyword>
     <SccAuxPath>
     </SccAuxPath>
+    <WindowsTargetPlatformVersion>10.0.17763.0</WindowsTargetPlatformVersion>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
     <ConfigurationType>Application</ConfigurationType>
     <CharacterSet>MultiByte</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">
     <ConfigurationType>Application</ConfigurationType>
     <CharacterSet>MultiByte</CharacterSet>
     <WholeProgramOptimization>false</WholeProgramOptimization>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Retail|Win32'" Label="Configuration">
     <ConfigurationType>Application</ConfigurationType>
     <CharacterSet>MultiByte</CharacterSet>
     <WholeProgramOptimization>false</WholeProgramOptimization>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
   <ImportGroup Label="ExtensionSettings">
@@ -101,15 +105,27 @@
     <ClCompile />
     <ClCompile />
     <ClCompile>
-      <TreatWarningAsError Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">true</TreatWarningAsError>
+      <TreatWarningAsError Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">false</TreatWarningAsError>
       <AdditionalIncludeDirectories Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">$(DXSDK_DIR)\Include\;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
+      <DiagnosticsFormat Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">Classic</DiagnosticsFormat>
+      <PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">Use</PrecompiledHeader>
+      <UndefinePreprocessorDefinitions Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
+      </UndefinePreprocessorDefinitions>
     </ClCompile>
     <ClCompile>
-      <TreatWarningAsError Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">true</TreatWarningAsError>
-      <TreatWarningAsError Condition="'$(Configuration)|$(Platform)'=='Retail|Win32'">true</TreatWarningAsError>
+      <TreatWarningAsError Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">false</TreatWarningAsError>
+      <TreatWarningAsError Condition="'$(Configuration)|$(Platform)'=='Retail|Win32'">false</TreatWarningAsError>
       <AdditionalIncludeDirectories Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">$(DXSDK_DIR)\Include\;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
       <AdditionalIncludeDirectories Condition="'$(Configuration)|$(Platform)'=='Retail|Win32'">$(DXSDK_DIR)\Include\;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
       <PreprocessorDefinitions Condition="'$(Configuration)|$(Platform)'=='Retail|Win32'">NDEBUG;%(PreprocessorDefinitions);ID_RETAIL</PreprocessorDefinitions>
+      <DiagnosticsFormat Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">Classic</DiagnosticsFormat>
+      <DiagnosticsFormat Condition="'$(Configuration)|$(Platform)'=='Retail|Win32'">Classic</DiagnosticsFormat>
+      <PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">Use</PrecompiledHeader>
+      <PrecompiledHeader Condition="'$(Configuration)|$(Platform)'=='Retail|Win32'">Use</PrecompiledHeader>
+      <UndefinePreprocessorDefinitions Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+      </UndefinePreprocessorDefinitions>
+      <UndefinePreprocessorDefinitions Condition="'$(Configuration)|$(Platform)'=='Retail|Win32'">
+      </UndefinePreprocessorDefinitions>
     </ClCompile>
     <ImageXex />
     <ImageXex />
diff --git a/neo/external.vcxproj b/neo/external.vcxproj
index 163b0e375..846d672a5 100644
--- a/neo/external.vcxproj
+++ b/neo/external.vcxproj
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+<Project DefaultTargets="Build" ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup Label="ProjectConfigurations">
     <ProjectConfiguration Include="Debug|Win32">
       <Configuration>Debug</Configuration>
@@ -97,24 +97,28 @@
     </SccLocalPath>
     <SccProvider>
     </SccProvider>
+    <WindowsTargetPlatformVersion>10.0.17763.0</WindowsTargetPlatformVersion>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
     <ConfigurationType>StaticLibrary</ConfigurationType>
     <UseDebugLibraries>true</UseDebugLibraries>
     <CharacterSet>Unicode</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">
     <ConfigurationType>StaticLibrary</ConfigurationType>
     <UseDebugLibraries>false</UseDebugLibraries>
     <WholeProgramOptimization>true</WholeProgramOptimization>
     <CharacterSet>Unicode</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Retail|Win32'" Label="Configuration">
     <ConfigurationType>StaticLibrary</ConfigurationType>
     <UseDebugLibraries>false</UseDebugLibraries>
     <WholeProgramOptimization>true</WholeProgramOptimization>
     <CharacterSet>Unicode</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
   <ImportGroup Label="ExtensionSettings">
diff --git a/neo/game-d3xp.vcxproj b/neo/game-d3xp.vcxproj
index c3e66593e..fed947b89 100644
--- a/neo/game-d3xp.vcxproj
+++ b/neo/game-d3xp.vcxproj
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+<Project DefaultTargets="Build" ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup Label="ProjectConfigurations">
     <ProjectConfiguration Include="Debug|Win32">
       <Configuration>Debug</Configuration>
@@ -27,19 +27,23 @@
     <Keyword>Win32Proj</Keyword>
     <SccAuxPath>
     </SccAuxPath>
+    <WindowsTargetPlatformVersion>10.0.17763.0</WindowsTargetPlatformVersion>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
     <ConfigurationType>StaticLibrary</ConfigurationType>
     <CharacterSet>MultiByte</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">
     <ConfigurationType>StaticLibrary</ConfigurationType>
     <CharacterSet>MultiByte</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Retail|Win32'" Label="Configuration">
     <ConfigurationType>StaticLibrary</ConfigurationType>
     <CharacterSet>MultiByte</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <PropertyGroup Label="Configuration" Condition="'$(Configuration)|$(Platform)'=='Debug with inlines|Xbox 360'">
     <ConfigurationType>DynamicLibrary</ConfigurationType>
@@ -89,7 +93,7 @@
     </PreBuildEvent>
     <Lib />
     <ClCompile>
-      <TreatWarningAsError>true</TreatWarningAsError>
+      <TreatWarningAsError>false</TreatWarningAsError>
     </ClCompile>
   </ItemDefinitionGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
@@ -98,7 +102,7 @@
       </Command>
     </PreBuildEvent>
     <ClCompile>
-      <TreatWarningAsError>true</TreatWarningAsError>
+      <TreatWarningAsError>false</TreatWarningAsError>
     </ClCompile>
   </ItemDefinitionGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Retail|Win32'">
@@ -107,7 +111,7 @@
       </Command>
     </PreBuildEvent>
     <ClCompile>
-      <TreatWarningAsError>true</TreatWarningAsError>
+      <TreatWarningAsError>false</TreatWarningAsError>
       <PreprocessorDefinitions>NDEBUG;%(PreprocessorDefinitions);ID_RETAIL</PreprocessorDefinitions>
     </ClCompile>
   </ItemDefinitionGroup>
diff --git a/neo/idlib.vcxproj b/neo/idlib.vcxproj
index 6db19f81f..9b6f88a25 100644
--- a/neo/idlib.vcxproj
+++ b/neo/idlib.vcxproj
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+<Project DefaultTargets="Build" ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup Label="ProjectConfigurations">
     <ProjectConfiguration Include="Debug|Win32">
       <Configuration>Debug</Configuration>
@@ -27,19 +27,23 @@
     <Keyword>Win32Proj</Keyword>
     <SccAuxPath>
     </SccAuxPath>
+    <WindowsTargetPlatformVersion>10.0.17763.0</WindowsTargetPlatformVersion>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
     <ConfigurationType>StaticLibrary</ConfigurationType>
     <CharacterSet>MultiByte</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">
     <ConfigurationType>StaticLibrary</ConfigurationType>
     <CharacterSet>MultiByte</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Retail|Win32'" Label="Configuration">
     <ConfigurationType>StaticLibrary</ConfigurationType>
     <CharacterSet>MultiByte</CharacterSet>
+    <PlatformToolset>v141</PlatformToolset>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
   <ImportGroup Label="ExtensionSettings">
@@ -78,17 +82,20 @@
   </PropertyGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
     <ClCompile>
-      <TreatWarningAsError>true</TreatWarningAsError>
+      <TreatWarningAsError>false</TreatWarningAsError>
+      <UndefinePreprocessorDefinitions>NONLS</UndefinePreprocessorDefinitions>
     </ClCompile>
   </ItemDefinitionGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
     <ClCompile>
-      <TreatWarningAsError>true</TreatWarningAsError>
+      <TreatWarningAsError>false</TreatWarningAsError>
+      <UndefinePreprocessorDefinitions>NONLS</UndefinePreprocessorDefinitions>
     </ClCompile>
   </ItemDefinitionGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Retail|Win32'">
     <ClCompile>
-      <TreatWarningAsError>true</TreatWarningAsError>
+      <TreatWarningAsError>false</TreatWarningAsError>
+      <UndefinePreprocessorDefinitions>NONLS</UndefinePreprocessorDefinitions>
     </ClCompile>
   </ItemDefinitionGroup>
   <ItemGroup>
diff --git a/neo/idlib/sys/sys_includes.h b/neo/idlib/sys/sys_includes.h
index 9aea3ff36..9b16e6fbb 100644
--- a/neo/idlib/sys/sys_includes.h
+++ b/neo/idlib/sys/sys_includes.h
@@ -44,8 +44,6 @@ If you have questions concerning this license or the applicable additional terms
 #ifndef _D3SDK
 #ifndef GAME_DLL
 
-#define WINVER				0x501
-
 #include <winsock2.h>
 #include <mmsystem.h>
 #include <mmreg.h>
diff --git a/neo/idlib/sys/sys_types.h b/neo/idlib/sys/sys_types.h
index 11acbf24b..bbe7754a9 100644
--- a/neo/idlib/sys/sys_types.h
+++ b/neo/idlib/sys/sys_types.h
@@ -86,13 +86,13 @@ class idFile;
 
 struct idNullPtr {
 	// one pointer member initialized to zero so you can pass NULL as a vararg
-	void *value; idNullPtr() : value( 0 ) { }
+	void *value; constexpr idNullPtr() : value( 0 ) { }
 
 	// implicit conversion to all pointer types
-	template<typename T1> operator T1 * () const { return 0; }
+	template<typename T1> constexpr operator T1 * () const { return 0; }
 
 	// implicit conversion to all pointer to member types
-	template<typename T1, typename T2> operator T1 T2::* () const { return 0; }
+	template<typename T1, typename T2> constexpr operator T1 T2::* () const { return 0; }
 };
 
 //#undef NULL