diff --git a/ide/vs2017/mimalloc-override.vcxproj b/ide/vs2017/mimalloc-override.vcxproj
index f3b7dd1e..f308225b 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\region.c" />
     <ClCompile Include="..\..\src\options.c" />
     <ClCompile Include="..\..\src\os.c" />
diff --git a/ide/vs2017/mimalloc-override.vcxproj.filters b/ide/vs2017/mimalloc-override.vcxproj.filters
index e045ed8c..a67dddad 100644
--- a/ide/vs2017/mimalloc-override.vcxproj.filters
+++ b/ide/vs2017/mimalloc-override.vcxproj.filters
@@ -82,5 +82,8 @@
     <ClCompile Include="..\..\src\bitmap.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 70bf4366..e7be785c 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\region.c" />
     <ClCompile Include="..\..\src\options.c" />
     <ClCompile Include="..\..\src\page-queue.c">
diff --git a/ide/vs2017/mimalloc.vcxproj.filters b/ide/vs2017/mimalloc.vcxproj.filters
index 500292c5..27cd4b5e 100644
--- a/ide/vs2017/mimalloc.vcxproj.filters
+++ b/ide/vs2017/mimalloc.vcxproj.filters
@@ -62,6 +62,9 @@
     <ClCompile Include="..\..\src\bitmap.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 36de1342..33aafa70 100644
--- a/include/mimalloc-internal.h
+++ b/include/mimalloc-internal.h
@@ -699,6 +699,7 @@ 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;