diff --git a/dev/00-gammalib-activate.sh b/dev/00-gammalib-activate.sh
index 68986a5..18b089e 100644
--- a/dev/00-gammalib-activate.sh
+++ b/dev/00-gammalib-activate.sh
@@ -2,3 +2,4 @@
 
 export GAMMALIB=${CONDA_PREFIX}
 source ${GAMMALIB}/bin/gammalib-init.sh
+unset PYTHONPATH