diff --git a/ide/vs2017/mimalloc-override.vcxproj b/ide/vs2017/mimalloc-override.vcxproj
index 05bd7223..bf0c7483 100644
--- a/ide/vs2017/mimalloc-override.vcxproj
+++ b/ide/vs2017/mimalloc-override.vcxproj
@@ -236,6 +236,7 @@
     <ClCompile Include="..\..\src\bitmap.c" />
     <ClCompile Include="..\..\src\heap.c" />
     <ClCompile Include="..\..\src\init.c" />
+    <ClCompile Include="..\..\src\prim\prim.c" />
     <ClCompile Include="..\..\src\options.c" />
     <ClCompile Include="..\..\src\os.c" />
     <ClCompile Include="..\..\src\page-queue.c">
diff --git a/ide/vs2017/mimalloc-override.vcxproj.filters b/ide/vs2017/mimalloc-override.vcxproj.filters
index d01f9311..1ba8cee4 100644
--- a/ide/vs2017/mimalloc-override.vcxproj.filters
+++ b/ide/vs2017/mimalloc-override.vcxproj.filters
@@ -82,5 +82,8 @@
     <ClCompile Include="..\..\src\segment-cache.c">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="..\..\src\prim\prim.c">
+      <Filter>Source Files</Filter>
+    </ClCompile>
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/ide/vs2017/mimalloc.vcxproj b/ide/vs2017/mimalloc.vcxproj
index 426bad1b..5fc3dffd 100644
--- a/ide/vs2017/mimalloc.vcxproj
+++ b/ide/vs2017/mimalloc.vcxproj
@@ -233,6 +233,7 @@
     <ClCompile Include="..\..\src\bitmap.c" />
     <ClCompile Include="..\..\src\heap.c" />
     <ClCompile Include="..\..\src\init.c" />
+    <ClCompile Include="..\..\src\prim\prim.c" />
     <ClCompile Include="..\..\src\options.c" />
     <ClCompile Include="..\..\src\page-queue.c">
       <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">true</ExcludedFromBuild>
diff --git a/ide/vs2017/mimalloc.vcxproj.filters b/ide/vs2017/mimalloc.vcxproj.filters
index 05417645..c3d53742 100644
--- a/ide/vs2017/mimalloc.vcxproj.filters
+++ b/ide/vs2017/mimalloc.vcxproj.filters
@@ -65,6 +65,9 @@
     <ClCompile Include="..\..\src\segment-cache.c">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="..\..\src\prim\prim.c">
+      <Filter>Source Files</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="$(ProjectDir)..\..\include\mimalloc.h">
diff --git a/ide/vs2019/mimalloc-override.vcxproj b/ide/vs2019/mimalloc-override.vcxproj
index 4c4235b4..7b6aada7 100644
--- a/ide/vs2019/mimalloc-override.vcxproj
+++ b/ide/vs2019/mimalloc-override.vcxproj
@@ -236,6 +236,7 @@
     <ClCompile Include="..\..\src\bitmap.c" />
     <ClCompile Include="..\..\src\heap.c" />
     <ClCompile Include="..\..\src\init.c" />
+    <ClCompile Include="..\..\src\prim\prim.c" />
     <ClCompile Include="..\..\src\options.c" />
     <ClCompile Include="..\..\src\os.c" />
     <ClCompile Include="..\..\src\page-queue.c">
diff --git a/ide/vs2019/mimalloc-override.vcxproj.filters b/ide/vs2019/mimalloc-override.vcxproj.filters
index d6b7b5a9..18237301 100644
--- a/ide/vs2019/mimalloc-override.vcxproj.filters
+++ b/ide/vs2019/mimalloc-override.vcxproj.filters
@@ -49,6 +49,9 @@
     <ClCompile Include="..\..\src\segment-cache.c">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="..\..\src\prim\prim.c" />
+      <Filter>Source Files</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="$(ProjectDir)..\..\include\mimalloc.h">
diff --git a/ide/vs2019/mimalloc.vcxproj b/ide/vs2019/mimalloc.vcxproj
index 209c7cb8..23030298 100644
--- a/ide/vs2019/mimalloc.vcxproj
+++ b/ide/vs2019/mimalloc.vcxproj
@@ -225,6 +225,7 @@
     </ClCompile>
     <ClCompile Include="..\..\src\heap.c" />
     <ClCompile Include="..\..\src\init.c" />
+    <ClCompile Include="..\..\src\prim\prim.c" />
     <ClCompile Include="..\..\src\options.c" />
     <ClCompile Include="..\..\src\page-queue.c">
       <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">true</ExcludedFromBuild>
diff --git a/ide/vs2019/mimalloc.vcxproj.filters b/ide/vs2019/mimalloc.vcxproj.filters
index 92be7cb4..46a7af9b 100644
--- a/ide/vs2019/mimalloc.vcxproj.filters
+++ b/ide/vs2019/mimalloc.vcxproj.filters
@@ -52,6 +52,9 @@
     <ClCompile Include="..\..\src\segment-cache.c">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="..\..\src\prim\prim.c">
+      <Filter>Source Files</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="$(ProjectDir)..\..\include\mimalloc.h">
diff --git a/include/mimalloc-internal.h b/include/mimalloc-internal.h
index 57564b79..3851187f 100644
--- a/include/mimalloc-internal.h
+++ b/include/mimalloc-internal.h
@@ -792,6 +792,7 @@ static inline size_t mi_ctz(uintptr_t x) {
 #elif defined(_MSC_VER)
 
 #include <limits.h>       // LONG_MAX
+#include <intrin.h>       // BitScanReverse64
 #define MI_HAVE_FAST_BITSCAN
 static inline size_t mi_clz(uintptr_t x) {
   if (x==0) return MI_INTPTR_BITS;