diff --git a/configure b/configure
index 4e150488224b..b57a2f0fbefe 100755
--- a/configure
+++ b/configure
@@ -1084,6 +1084,65 @@ do
                 err "musl libc $CFG_MUSL_ROOT/lib/libc.a not found"
             fi
             ;;
+
+        x86_64-*-msvc)
+            # Currently the build system is not configured to build jemalloc
+            # with MSVC, so we omit this optional dependency.
+            step_msg "targeting MSVC, disabling jemalloc"
+            CFG_DISABLE_JEMALLOC=1
+            putvar CFG_DISABLE_JEMALLOC
+
+            # There are some MSYS python builds which will auto-translate
+            # windows-style paths to MSYS-style paths in Python itself.
+            # Unfortunately this breaks LLVM's build system as somewhere along
+            # the line LLVM prints a path into a file from Python and then CMake
+            # later tries to interpret that path. If Python prints a MSYS path
+            # and CMake tries to use it as a Windows path, you're gonna have a
+            # Bad Time.
+            #
+            # Consequently here we try to detect when that happens and print an
+            # error if it does.
+            if $CFG_PYTHON -c 'import sys; print sys.argv[1]' `pwd` | grep '^/'
+            then
+                err "python is silently translating windows paths to MSYS paths \
+                     and the build will fail if this python is used.\n\n \
+                     Either an official python install must be used or an \
+                     alternative python package in MinGW must be used."
+            fi
+
+            # MSVC requires cmake because that's how we're going to build LLVM
+            probe_need CFG_CMAKE cmake
+
+            # Use the REG program to figure out where VS is installed
+            # We need to figure out where cl.exe and link.exe are, so we do some
+            # munging and some probing here. We also look for the default
+            # INCLUDE and LIB variables for MSVC so we can set those in the
+            # build system as well.
+            install=$(reg QUERY \
+                       'HKLM\SOFTWARE\Wow6432Node\Microsoft\VisualStudio\12.0' \
+                       -v InstallDir)
+            need_ok "couldn't find visual studio install root"
+            CFG_MSVC_ROOT=$(echo "$install" | grep InstallDir | sed 's/.*REG_SZ[ ]*//')
+            CFG_MSVC_ROOT=$(dirname "$CFG_MSVC_ROOT")
+            CFG_MSVC_ROOT=$(dirname "$CFG_MSVC_ROOT")
+            CFG_MSVC_CL="${CFG_MSVC_ROOT}/VC/bin/amd64/cl.exe"
+            CFG_MSVC_LIB="${CFG_MSVC_ROOT}/VC/bin/amd64/lib.exe"
+            CFG_MSVC_LINK="${CFG_MSVC_ROOT}/VC/bin/amd64/link.exe"
+
+            vcvarsall="${CFG_MSVC_ROOT}/VC/vcvarsall.bat"
+            CFG_MSVC_INCLUDE_PATH=$(cmd /c "\"$vcvarsall\" amd64 && cmd /c echo %INCLUDE%")
+            need_ok "failed to learn about MSVC's INCLUDE"
+            CFG_MSVC_LIB_PATH=$(cmd /c "\"$vcvarsall\" amd64 && cmd /c echo %LIB%")
+            need_ok "failed to learn about MSVC's LIB"
+
+            putvar CFG_MSVC_ROOT
+            putvar CFG_MSVC_CL
+            putvar CFG_MSVC_LIB
+            putvar CFG_MSVC_LINK
+            putvar CFG_MSVC_INCLUDE_PATH
+            putvar CFG_MSVC_LIB_PATH
+            ;;
+
         *)
             ;;
     esac
@@ -1125,6 +1184,7 @@ do
   do
     make_dir $t/rt/stage$s
     make_dir $t/rt/jemalloc
+    make_dir $t/rt/compiler-rt
     for i in                                          \
       isaac sync test \
       arch/i386 arch/x86_64 arch/arm arch/aarch64 arch/mips arch/powerpc
@@ -1496,11 +1556,6 @@ do
     putvar $CFG_LLVM_INST_DIR
 done
 
-# Munge any paths that appear in config.mk back to posix-y
-cp config.tmp config.tmp.bak
-sed -e 's@ \([a-zA-Z]\):[/\\]@ /\1/@g;' <config.tmp.bak >config.tmp
-rm -f config.tmp.bak
-
 msg
 copy_if_changed ${CFG_SRC_DIR}Makefile.in ./Makefile
 move_if_changed config.tmp config.mk
diff --git a/mk/cfg/x86_64-pc-windows-msvc.mk b/mk/cfg/x86_64-pc-windows-msvc.mk
index 4a77b658d46f..4e97ae3abe11 100644
--- a/mk/cfg/x86_64-pc-windows-msvc.mk
+++ b/mk/cfg/x86_64-pc-windows-msvc.mk
@@ -1,9 +1,9 @@
 # x86_64-pc-windows-msvc configuration
-CC_x86_64-pc-windows-msvc=cl
-LINK_x86_64-pc-windows-msvc=link
-CXX_x86_64-pc-windows-msvc=cl
-CPP_x86_64-pc-windows-msvc=cl
-AR_x86_64-pc-windows-msvc=llvm-ar
+CC_x86_64-pc-windows-msvc="$(CFG_MSVC_CL)" -nologo
+LINK_x86_64-pc-windows-msvc="$(CFG_MSVC_LINK)" -nologo
+CXX_x86_64-pc-windows-msvc="$(CFG_MSVC_CL)" -nologo
+CPP_x86_64-pc-windows-msvc="$(CFG_MSVC_CL)" -nologo
+AR_x86_64-pc-windows-msvc="$(CFG_MSVC_LIB)" -nologo
 CFG_LIB_NAME_x86_64-pc-windows-msvc=$(1).dll
 CFG_STATIC_LIB_NAME_x86_64-pc-windows-msvc=$(1).lib
 CFG_LIB_GLOB_x86_64-pc-windows-msvc=$(1)-*.dll
@@ -21,4 +21,21 @@ CFG_UNIXY_x86_64-pc-windows-msvc :=
 CFG_LDPATH_x86_64-pc-windows-msvc :=
 CFG_RUN_x86_64-pc-windows-msvc=$(2)
 CFG_RUN_TARG_x86_64-pc-windows-msvc=$(call CFG_RUN_x86_64-pc-windows-msvc,,$(2))
-CFG_GNU_TRIPLE_x86_64-pc-windows-msvc := x86_64-pc-windows-msvc
+CFG_GNU_TRIPLE_x86_64-pc-windows-msvc := x86_64-pc-win32
+
+# These two environment variables are scraped by the `./configure` script and
+# are necessary for `cl.exe` to find standard headers (the INCLUDE variable) and
+# for `link.exe` to find standard libraries (the LIB variable).
+ifdef CFG_MSVC_INCLUDE_PATH
+export INCLUDE := $(CFG_MSVC_INCLUDE_PATH)
+endif
+ifdef CFG_MSVC_LIB_PATH
+export LIB := $(CFG_MSVC_LIB_PATH)
+endif
+
+# Unfortunately `link.exe` is also a program in `/usr/bin` on MinGW installs,
+# but it's not the one that we want. As a result we make sure that our detected
+# `link.exe` shows up in PATH first.
+ifdef CFG_MSVC_LINK
+export PATH := $(CFG_MSVC_ROOT)/VC/bin/amd64:$(PATH)
+endif