diff --git a/pulsar.sh b/pulsar.sh
index 6fd4615ce..e3dab18cd 100755
--- a/pulsar.sh
+++ b/pulsar.sh
@@ -10,7 +10,10 @@ else
 fi
 
 # Only set the ATOM_DISABLE_SHELLING_OUT_FOR_ENVIRONMENT env var if it hasn't been set.
-: ${ATOM_DISABLE_SHELLING_OUT_FOR_ENVIRONMENT:=true}
+if [ -z "$ATOM_DISABLE_SHELLING_OUT_FOR_ENVIRONMENT" ]
+then
+  export ATOM_DISABLE_SHELLING_OUT_FOR_ENVIRONMENT=true
+fi
 
 ATOM_ADD=false
 ATOM_NEW_WINDOW=false