diff --git a/clean_build.sh b/clean_build.sh
index d73d39672..032316082 100755
--- a/clean_build.sh
+++ b/clean_build.sh
@@ -17,7 +17,7 @@ B_CMAKE_FLAGS="-DCMAKE_BUILD_TYPE=${B_BUILD_TYPE} ${B_CMAKE_FLAGS:-}"
 
 if [ "$(uname)" = "Darwin" ]; then
     # macOS needs a little help, so we source this environment script to fix paths.
-    . ./macos_environment.sh
+    [ -e ./macos_environment.sh ] && . ./macos_environment.sh
     B_CMAKE_FLAGS="${B_CMAKE_FLAGS} -DCMAKE_OSX_SYSROOT=$(xcode-select --print-path)/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk -DCMAKE_OSX_DEPLOYMENT_TARGET=10.9"
 fi