diff --git a/ci/test-nightly.sh b/ci/test-nightly.sh
index 5689ea45e039c6..7f6b520f288d29 100755
--- a/ci/test-nightly.sh
+++ b/ci/test-nightly.sh
@@ -28,9 +28,9 @@ maybe_cargo_install() {
 maybe_cargo_install cov
 
 if [[ ! -f ./grcov ]]; then
-  uname=$(uname)
-  uname_m=$(uname -m)
-  name=grcov-${uname//A-Z/a-z}-${uname_m//A-Z/a-z}
+  uname=$(uname | tr '[:upper:]' '[:lower:]')
+  uname_m=$(uname -m | tr '[:upper:]' '[:lower:]')
+  name=grcov-${uname}-${uname_m}
   _ wget "https://github.com/mozilla/grcov/releases/download/v0.2.3/${name}"
   _ tar -xzf "${name}"
 fi