diff --git a/tests/functional/nix-shell.sh b/tests/functional/nix-shell.sh
index 3343d6195..263679347 100755
--- a/tests/functional/nix-shell.sh
+++ b/tests/functional/nix-shell.sh
@@ -39,8 +39,8 @@ testTmpDir=$(pwd)/nix-shell
 mkdir -p "$testTmpDir"
 # shellcheck disable=SC2016
 output=$(TMPDIR="$testTmpDir" nix-shell --pure "$shellDotNix" -A shellDrv --run 'echo $NIX_BUILD_TOP')
-[[ "$output" =~ ${testTmpDir}.* ]] || {
-    echo "expected $output =~ ${testTmpDir}.*" >&2
+[[ "$output" == "${testTmpDir}"/* ]] || {
+    echo "expected $output == ${testTmpDir}/*" >&2
     exit 1
 }