diff --git a/micromamba/etc/profile.d/mamba.sh.in b/micromamba/etc/profile.d/mamba.sh.in
index 5980ed391c..f1bea69204 100644
--- a/micromamba/etc/profile.d/mamba.sh.in
+++ b/micromamba/etc/profile.d/mamba.sh.in
@@ -1,4 +1,4 @@
-if [ ! -v MAMBA_ROOT_PREFIX ]; then
+if [ -z "${MAMBA_ROOT_PREFIX:-}" ]; then
     echo "WARNING: The MAMBA_ROOT_PREFIX environment variable is not set."
     echo "WARNING: This is required for mamba to work correctly as of 2.0."
     echo "WARNING: "