diff --git a/CMakeLists.txt b/CMakeLists.txt
index 63751d6..1035201 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -217,17 +217,8 @@
 endif( CMAKE_SIZEOF_VOID_P EQUAL 8 AND NOT WIN32 )
 
 if( MSVC )
-  # List of valid CRTs for MSVC
-  set(MSVC_CRT
-    MD
-    MDd
-    MT
-    MTd)
+  include(ChooseMSVCCRT)
 
-  set(LLVM_USE_CRT "" CACHE STRING "Specify VC++ CRT to use for debug/release configurations.")
-  # Lets the GUI show a drop-down list of possible values, including
-  # an empty string as the default:
-  set_property(CACHE LLVM_USE_CRT PROPERTY STRINGS "";${MSVC_CRT})
   add_llvm_definitions( -D_CRT_SECURE_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS )
   add_llvm_definitions( -D_SCL_SECURE_NO_WARNINGS -DCRT_NONSTDC_NO_WARNINGS )
   add_llvm_definitions( -D_SCL_SECURE_NO_DEPRECATE )
@@ -237,15 +228,6 @@
   # Suppress 'new behavior: elements of array 'array' will be default initialized'
   add_llvm_definitions( -wd4351 )
 
-  if (NOT ${LLVM_USE_CRT} STREQUAL "")
-    list(FIND MSVC_CRT ${LLVM_USE_CRT} idx)
-    if (idx LESS 0)
-      message(FATAL_ERROR "Invalid value for LLVM_USE_CRT: ${LLVM_USE_CRT}. Valid options are one of: ${MSVC_CRT}")
-    endif (idx LESS 0)
-    add_llvm_definitions("/${LLVM_USE_CRT}")
-    message(STATUS "Using VC++ CRT: ${LLVM_USE_CRT}")
-  endif (NOT ${LLVM_USE_CRT} STREQUAL "")
-
   # Enable warnings
   if (LLVM_ENABLE_WARNINGS)
     add_llvm_definitions( /W4 /Wall )
diff --git a/cmake/modules/ChooseMSVCCRT.cmake b/cmake/modules/ChooseMSVCCRT.cmake
new file mode 100644
index 0000000..eb78f45
--- /dev/null
+++ b/cmake/modules/ChooseMSVCCRT.cmake
@@ -0,0 +1,106 @@
+# The macro choose_msvc_crt() takes a list of possible
+# C runtimes to choose from, in the form of compiler flags,
+# to present to the user. (MTd for /MTd, etc)
+#
+# The macro is invoked at the end of the file.
+#
+# CMake already sets CRT flags in the CMAKE_CXX_FLAGS_* and
+# CMAKE_C_FLAGS_* variables by default. To let the user
+# override that for each build type:
+# 1. Detect which CRT is already selected, and reflect this in
+# LLVM_USE_CRT_* so the user can have a better idea of what
+# changes they're making.
+# 2. Replace the flags in both variables with the new flag via a regex.
+# 3. set() the variables back into the cache so the changes
+# are user-visible.
+
+### Helper macros: ###
+macro(make_crt_regex regex crts)
+  set(${regex} "")
+  foreach(crt ${${crts}})
+    # Trying to match the beginning or end of the string with stuff
+    # like [ ^]+ didn't work, so use a bunch of parentheses instead.
+    set(${regex} "${${regex}}|(^| +)/${crt}($| +)")
+  endforeach(crt)
+  string(REGEX REPLACE "^\\|" "" ${regex} "${${regex}}")
+endmacro(make_crt_regex)
+
+macro(get_current_crt crt_current regex flagsvar)
+  # Find the selected-by-CMake CRT for each build type, if any.
+  # Strip off the leading slash and any whitespace.
+  string(REGEX MATCH "${${regex}}" ${crt_current} "${${flagsvar}}")
+  string(REPLACE "/" " " ${crt_current} "${${crt_current}}")
+  string(STRIP "${${crt_current}}" ${crt_current})
+endmacro(get_current_crt)
+
+# Replaces or adds a flag to a variable.
+# Expects 'flag' to be padded with spaces.
+macro(set_flag_in_var flagsvar regex flag)
+  string(REGEX MATCH "${${regex}}" current_flag "${${flagsvar}}")
+  if("${current_flag}" STREQUAL "")
+    set(${flagsvar} "${${flagsvar}}${${flag}}")
+  else()
+    string(REGEX REPLACE "${${regex}}" "${${flag}}" ${flagsvar} "${${flagsvar}}")
+  endif()
+  string(STRIP "${${flagsvar}}" ${flagsvar})
+  # Make sure this change gets reflected in the cache/gui.
+  # CMake requires the docstring parameter whenever set() touches the cache,
+  # so get the existing docstring and re-use that.
+  get_property(flagsvar_docs CACHE ${flagsvar} PROPERTY HELPSTRING)
+  set(${flagsvar} "${${flagsvar}}" CACHE STRING "${flagsvar_docs}" FORCE)
+endmacro(set_flag_in_var)
+
+
+macro(choose_msvc_crt MSVC_CRT)
+  if(LLVM_USE_CRT)
+    message(FATAL_ERROR
+      "LLVM_USE_CRT is deprecated. Use the CMAKE_BUILD_TYPE-specific
+variables (LLVM_USE_CRT_DEBUG, etc) instead.")
+  endif()
+
+  make_crt_regex(MSVC_CRT_REGEX ${MSVC_CRT})
+
+  foreach(build_type ${CMAKE_CONFIGURATION_TYPES})
+    string(TOUPPER "${build_type}" build)
+    if (NOT LLVM_USE_CRT_${build})
+      get_current_crt(LLVM_USE_CRT_${build}
+	MSVC_CRT_REGEX
+	CMAKE_CXX_FLAGS_${build})
+      set(LLVM_USE_CRT_${build}
+	"${LLVM_USE_CRT_${build}}"
+	CACHE STRING "Specify VC++ CRT to use for ${build_type} configurations."
+	FORCE)
+      set_property(CACHE LLVM_USE_CRT_${build}
+	PROPERTY STRINGS "";${${MSVC_CRT}})
+    endif(NOT LLVM_USE_CRT_${build})
+  endforeach(build_type)
+
+  foreach(build_type ${CMAKE_CONFIGURATION_TYPES})
+    string(TOUPPER "${build_type}" build)
+    if ("${LLVM_USE_CRT_${build}}" STREQUAL "")
+      set(flag_string " ")
+    else()
+      set(flag_string " /${LLVM_USE_CRT_${build}} ")
+      list(FIND ${MSVC_CRT} ${LLVM_USE_CRT_${build}} idx)
+      if (idx LESS 0)
+        message(FATAL_ERROR
+	  "Invalid value for LLVM_USE_CRT_${build}: ${LLVM_USE_CRT_${build}}. Valid options are one of: ${${MSVC_CRT}}")
+      endif (idx LESS 0)
+      message(STATUS "Using ${build_type} VC++ CRT: ${LLVM_USE_CRT_${build}}")
+    endif()
+    foreach(lang C CXX)
+      set_flag_in_var(CMAKE_${lang}_FLAGS_${build} MSVC_CRT_REGEX flag_string)
+    endforeach(lang)
+  endforeach(build_type)
+endmacro(choose_msvc_crt MSVC_CRT)
+
+
+# List of valid CRTs for MSVC
+set(MSVC_CRT
+  MD
+  MDd
+  MT
+  MTd)
+
+choose_msvc_crt(MSVC_CRT)
+