diff --git a/binary_tarball/scripts/3_Configure_Source_Code.sh b/binary_tarball/scripts/3_Configure_Source_Code.sh
index 37f5bd8..49ac61a 100755
--- a/binary_tarball/scripts/3_Configure_Source_Code.sh
+++ b/binary_tarball/scripts/3_Configure_Source_Code.sh
@@ -20,6 +20,10 @@ cd $srcdir
 cat >${CI_PROJECT_DIR}/mozconfig <<END
 ac_add_options --enable-application=browser
 
+# to build on ubuntu and pick up clang
+ac_add_options --with-libclang-path="/usr/lib/${CARCH}-linux-gnu/libclang-cpp.so.9"
+ac_add_options --with-clang-path="/usr/bin/clang-9"
+
 # This supposedly speeds up compilation (We test through dogfooding anyway)
 ac_add_options --disable-tests
 ac_add_options --disable-debug
@@ -30,12 +34,11 @@ ac_add_options --enable-release
 ac_add_options --enable-hardening
 ac_add_options --enable-rust-simd
 
-# let mach bootstrap do its thing instead
-# export CC='clang-9'
-# export CXX='clang++-9'
-# export AR=llvm-ar-9
-# export NM=llvm-nm-9
-# export RANLIB=llvm-ranlib-9
+export CC='clang-9'
+export CXX='clang++-9'
+export AR=llvm-ar-9
+export NM=llvm-nm-9
+export RANLIB=llvm-ranlib-9
 
 # Branding
 ac_add_options --enable-update-channel=release