diff --git a/.gitignore b/.gitignore
index ba5df6d8..4000ad56 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
 winbuild_env.bat
+unixbuild_env.sh
 config.h
 .DS_Store
 *.pyc
diff --git a/clean_build.sh b/clean_build.sh
index f5438598..cdd81fbd 100755
--- a/clean_build.sh
+++ b/clean_build.sh
@@ -1,8 +1,5 @@
 #!/bin/sh
 cd "$(dirname $0)" || exit 1
-rm -rf build
-mkdir build || exit 1
-cd build || exit 1
 # some environments have cmake v2 as 'cmake' and v3 as 'cmake3'
 # check for cmake3 first then fallback to just cmake
 B_CMAKE=`type cmake3 2>/dev/null`
@@ -16,10 +13,15 @@ B_BUILD_TYPE=${B_BUILD_TYPE:-Debug}
 if [ "$(uname)" = "Darwin" ]; then
     # OSX needs a lot of extra help, poor thing
     # run the osx_environment.sh script to fix paths
-    [ -r ../osx_environment.sh ] && source ../osx_environment.sh
+    source ./osx_environment.sh
     B_CMAKE_FLAGS="-DCMAKE_OSX_SYSROOT=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk -DCMAKE_OSX_DEPLOYMENT_TARGET=10.9 $B_CMAKE_FLAGS"
 fi
 B_CMAKE_FLAGS="-DCMAKE_BUILD_TYPE=$B_BUILD_TYPE $B_CMAKE_FLAGS"
+# allow local customizations to build environment
+[ -r ./unixbuild_env.sh ] && source ./unixbuild_env.sh
+rm -rf build
+mkdir build || exit 1
+cd build || exit 1
 echo Starting Barrier $B_BUILD_TYPE build...
 $B_CMAKE $B_CMAKE_FLAGS .. || exit 1
 make || exit 1