diff --git a/cpp/cmake_modules/CompilerInfo.cmake b/cpp/cmake_modules/CompilerInfo.cmake
index 4a18376df59..a1b470182a8 100644
--- a/cpp/cmake_modules/CompilerInfo.cmake
+++ b/cpp/cmake_modules/CompilerInfo.cmake
@@ -68,6 +68,11 @@ elseif("${COMPILER_VERSION_FULL}" MATCHES ".*clang-8")
   set(COMPILER_FAMILY "clang")
   set(COMPILER_VERSION "3.8.0svn")
 
+# clang on Mac OS X, XCode 8.
+elseif("${COMPILER_VERSION_FULL}" MATCHES ".*clang-9")
+  set(COMPILER_FAMILY "clang")
+  set(COMPILER_VERSION "4.0.0svn")
+
 # gcc
 elseif("${COMPILER_VERSION_FULL_LOWER}" MATCHES ".*gcc[ -]version.*")
   set(COMPILER_FAMILY "gcc")