diff --git a/lib/builtins/CMakeLists.txt b/lib/builtins/CMakeLists.txt
index 25bd921fcb..571137a0b2 100644
--- a/lib/builtins/CMakeLists.txt
+++ b/lib/builtins/CMakeLists.txt
@@ -361,11 +361,18 @@ else ()
         endif ()
       endforeach ()
 
+      # Rust: don't insert a reference to MSVCRT.lib/etc
+      if (MSVC)
+        set(_cflags -Zl)
+      else ()
+        set(_cflags -std=c99)
+      endif ()
+
       add_compiler_rt_runtime(clang_rt.builtins
                               STATIC
                               ARCHS ${arch}
                               SOURCES ${${arch}_SOURCES}
-                              CFLAGS "-std=c99"
+                              CFLAGS ${_cflags}
                               PARENT_TARGET builtins)
     endif ()
   endforeach ()
diff --git a/lib/builtins/int_math.h b/lib/builtins/int_math.h
index fc81fb7f02..9a8b751e44 100644
--- a/lib/builtins/int_math.h
+++ b/lib/builtins/int_math.h
@@ -28,7 +28,9 @@
 #if defined(_MSC_VER) && !defined(__clang__)
 #include <math.h>
 #include <stdlib.h>
-#include <ymath.h>
+// Rust: need to upstream this
+// don't include ymath.h, it's not needed + pulls in the C++ stdlib for some reason
+// #include <ymath.h>
 #endif
 
 #if defined(_MSC_VER) && !defined(__clang__)
diff --git a/make/platform/triple.mk b/make/platform/triple.mk
index 7e3450e395..0d68b2eafd 100644
--- a/make/platform/triple.mk
+++ b/make/platform/triple.mk
@@ -60,6 +60,12 @@ ifneq (,$(findstring mips,$(TargetTriple)))
     CommonDisabledFunctions := emutls
 endif
 
+# Disable emutls on Windows
+# emutls works on POSIX only as it uses pthreads
+ifneq (,$(findstring windows,$(TargetTriple)))
+    CommonDisabledFunctions := emutls
+endif
+
 # Clear cache is builtin on aarch64-apple-ios
 # arm64 and aarch64 are synonims, but iOS targets usually use arm64 (history reasons)
 ifeq (aarch64-apple-ios,$(subst arm64,aarch64,$(TargetTriple)))