diff --git a/clean_build.sh b/clean_build.sh
index f78bc463..3a92d8b9 100755
--- a/clean_build.sh
+++ b/clean_build.sh
@@ -14,7 +14,7 @@ if [ "$(uname)" = "Darwin" ]; then
     # OSX needs a lot of extra help, poor thing
     # run the osx_environment.sh script to fix paths
     . ./osx_environment.sh
-    B_CMAKE_FLAGS="-DCMAKE_OSX_SYSROOT=$(xcode-select --print-path)/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk -DCMAKE_OSX_DEPLOYMENT_TARGET=11.0 $B_CMAKE_FLAGS"
+    B_CMAKE_FLAGS="-DCMAKE_OSX_SYSROOT=$(xcode-select --print-path)/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk -DCMAKE_OSX_DEPLOYMENT_TARGET=10.9 $B_CMAKE_FLAGS"
 fi
 # allow local customizations to build environment
 [ -r ./build_env.sh ] && . ./build_env.sh