diff --git a/build_sysroot/build_sysroot.sh b/build_sysroot/build_sysroot.sh
index 063219aabd2..6aea9b94b48 100755
--- a/build_sysroot/build_sysroot.sh
+++ b/build_sysroot/build_sysroot.sh
@@ -30,9 +30,9 @@ mkdir -p sysroot/lib/rustlib/$TARGET_TRIPLE/lib/
 cp -r target/$TARGET_TRIPLE/$sysroot_channel/deps/* sysroot/lib/rustlib/$TARGET_TRIPLE/lib/
 
 # Since we can't override the sysroot for the UI tests anymore, we create a new toolchain and manually overwrite the sysroot directory.
-my_toolchain_dir=$HOME/.rustup/toolchains/codegen_gcc_ui_tests
-rm -rf $my_toolchain_dir
 rust_toolchain=$(cat ../rust-toolchain | grep channel | sed 's/channel = "\(.*\)"/\1/')
+my_toolchain_dir=$HOME/.rustup/toolchains/codegen_gcc_ui_tests-$rust_toolchain-$TARGET_TRIPLE
+rm -rf $my_toolchain_dir
 cp -r $HOME/.rustup/toolchains/$rust_toolchain-$TARGET_TRIPLE $my_toolchain_dir
 rm -rf $my_toolchain_dir/lib/rustlib/$TARGET_TRIPLE/
 cp -r ../build_sysroot/sysroot/* $my_toolchain_dir
diff --git a/test.sh b/test.sh
index 6213ed49183..2e485b92739 100755
--- a/test.sh
+++ b/test.sh
@@ -209,11 +209,12 @@ function setup_rustc() {
     cd rust
     git fetch
     git checkout $(rustc -V | cut -d' ' -f3 | tr -d '(')
+    git am ../0001-Allow-overwriting-the-sysroot-compile-flag-via-rustc.patch
     export RUSTFLAGS=
 
     rm config.toml || true
 
-    my_toolchain_dir=$HOME/.rustup/toolchains/codegen_gcc_ui_tests
+    my_toolchain_dir=$HOME/.rustup/toolchains/codegen_gcc_ui_tests-$rust_toolchain-$TARGET_TRIPLE
 
     cat > config.toml <<EOF
 changelog-seen = 2
@@ -222,12 +223,13 @@ changelog-seen = 2
 codegen-backends = []
 deny-warnings = false
 
+# FIXME: it works with the original rustc and cargo.
 [build]
-cargo = "$my_toolchain_dir/bin/cargo"
-#cargo = "$(rustup which cargo)"
+#cargo = "$my_toolchain_dir/bin/cargo"
+cargo = "$(rustup which cargo)"
 local-rebuild = true
-rustc = "$my_toolchain_dir/bin/rustc"
-#rustc = "$HOME/.rustup/toolchains/$rust_toolchain-$TARGET_TRIPLE/bin/rustc"
+#rustc = "$my_toolchain_dir/bin/rustc"
+rustc = "$HOME/.rustup/toolchains/$rust_toolchain-$TARGET_TRIPLE/bin/rustc"
 
 [target.x86_64-unknown-linux-gnu]
 llvm-filecheck = "`which FileCheck-10 || which FileCheck-11 || which FileCheck-12 || which FileCheck-13 || which FileCheck-14`"
@@ -359,7 +361,7 @@ function test_rustc() {
     git checkout tests/ui/type-alias-impl-trait/auxiliary/cross_crate_ice2.rs
     git checkout tests/ui/macros/rfc-2011-nicer-assert-messages/auxiliary/common.rs
 
-    RUSTC_ARGS="$TEST_FLAGS -Csymbol-mangling-version=v0 -Zcodegen-backend="$(pwd)"/../target/"$CHANNEL"/librustc_codegen_gcc."$dylib_ext""
+    RUSTC_ARGS="$TEST_FLAGS -Csymbol-mangling-version=v0 -Zcodegen-backend="$(pwd)"/../target/"$CHANNEL"/librustc_codegen_gcc."$dylib_ext" --sysroot "$(pwd)"/../build_sysroot/sysroot"
 
 
     if [ $# -eq 0 ]; then
@@ -392,6 +394,7 @@ function test_rustc() {
     fi
 
     echo "[TEST] rustc test suite"
+    # FIXME: the problem seems like an ABI incompatibility between cg_gcc sysroot and cg_llvm.
     COMPILETEST_FORCE_STAGE0=1 ./x.py test --run always --stage 0 tests/ui --rustc-args "$RUSTC_ARGS"
 }