diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -143,6 +143,20 @@
   endif()
 endif()
 
+# Select the runtimes to build
+set(LLVM_DEFAULT_RUNTIMES "compiler-rt;libc;libcxx;libcxxabi;libunwind;openmp")
+set(LLVM_SUPPORTED_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;llvm-libgcc")
+set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
+  "Semicolon-separated list of runtimes to build, or \"all\" (${LLVM_DEFAULT_RUNTIMES}). Supported runtimes are ${LLVM_SUPPORTED_RUNTIMES}.")
+if(LLVM_ENABLE_RUNTIMES STREQUAL "all")
+  set(LLVM_ENABLE_RUNTIMES ${LLVM_DEFAULT_RUNTIMES})
+endif()
+foreach(proj IN LISTS LLVM_ENABLE_RUNTIMES)
+  if (NOT "${proj}" IN_LIST LLVM_SUPPORTED_RUNTIMES)
+    message(FATAL_ERROR "Runtime ${proj} is not a supported runtime. Supported runtimes are: ${LLVM_SUPPORTED_RUNTIMES}")
+  endif()
+endforeach()
+
 # LLVM_ENABLE_PROJECTS_USED is `ON` if the user has ever used the
 # `LLVM_ENABLE_PROJECTS` CMake cache variable.  This exists for
 # several reasons:
diff --git a/llvm/runtimes/CMakeLists.txt b/llvm/runtimes/CMakeLists.txt
--- a/llvm/runtimes/CMakeLists.txt
+++ b/llvm/runtimes/CMakeLists.txt
@@ -3,16 +3,6 @@
 # similar although simpler functionality. We should figure out how to merge
 # the two files.
 
-# TODO: Selecting runtimes should be always performed inside the runtimes
-# build, see runtimes/CMakeLists.txt, except that we currently check whether
-# compiler-rt is being built to determine whether to first build builtins
-# or not so we need that information in this file as well.
-set(LLVM_ALL_RUNTIMES "compiler-rt;libc;libcxx;libcxxabi;libunwind;openmp")
-set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
-  "Semicolon-separated list of runtimes to build (${LLVM_ALL_RUNTIMES}), or \"all\".")
-if(LLVM_ENABLE_RUNTIMES STREQUAL "all" )
-  set(LLVM_ENABLE_RUNTIMES ${LLVM_ALL_RUNTIMES})
-endif()
 set(COMMON_CMAKE_ARGS "-DHAVE_LLVM_LIT=ON")
 foreach(proj ${LLVM_ENABLE_RUNTIMES})
   set(proj_dir "${CMAKE_CURRENT_SOURCE_DIR}/../../${proj}")
diff --git a/runtimes/CMakeLists.txt b/runtimes/CMakeLists.txt
--- a/runtimes/CMakeLists.txt
+++ b/runtimes/CMakeLists.txt
@@ -16,14 +16,14 @@
 # We order libraries to mirror roughly how they are layered, except that compiler-rt can depend
 # on libc++, so we put it after.
 set(LLVM_DEFAULT_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp")
-set(LLVM_ALL_RUNTIMES "${LLVM_DEFAULT_RUNTIMES};llvm-libgcc")
+set(LLVM_SUPPORTED_RUNTIMES "${LLVM_DEFAULT_RUNTIMES};llvm-libgcc")
 set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
-  "Semicolon-separated list of runtimes to build (${LLVM_ALL_RUNTIMES}), or \"all\".")
+  "Semicolon-separated list of runtimes to build, or \"all\" (${LLVM_DEFAULT_RUNTIMES}). Supported runtimes are ${LLVM_SUPPORTED_RUNTIMES}.")
 if(LLVM_ENABLE_RUNTIMES STREQUAL "all" )
   set(LLVM_ENABLE_RUNTIMES ${LLVM_DEFAULT_RUNTIMES})
 endif()
 include(SortSubset)
-sort_subset("${LLVM_ALL_RUNTIMES}" "${LLVM_ENABLE_RUNTIMES}" LLVM_ENABLE_RUNTIMES)
+sort_subset("${LLVM_SUPPORTED_RUNTIMES}" "${LLVM_ENABLE_RUNTIMES}" LLVM_ENABLE_RUNTIMES)
 
 foreach(proj ${LLVM_ENABLE_RUNTIMES})
   set(proj_dir "${CMAKE_CURRENT_SOURCE_DIR}/../${proj}")