diff --git a/setup.sh b/setup.sh
index 0cc0626..3e46249 100755
--- a/setup.sh
+++ b/setup.sh
@@ -208,7 +208,9 @@ ok "Conda environment created."
 
 # We need to source conda's shell hook to use `conda activate` in a script
 eval "$(conda shell.bash hook)"
+set +u # Allow referencing unset variables for the conda activation script (e.g. GFORTRAN)
 conda activate "${ENV_ACTIVATE}"
+set -u
 
 CONDA_PREFIX="${CONDA_PREFIX}"
 info "CONDA_PREFIX = ${CONDA_PREFIX}"