diff --git a/scripts/_common.sh b/scripts/_common.sh
index f760389..edc919b 100755
--- a/scripts/_common.sh
+++ b/scripts/_common.sh
@@ -49,9 +49,10 @@ install_sources() {
         # Install synapse in virtualenv
 
         # We set all necessary environement variable to create a python virtualenvironnement.
-        set +u;
+        u_arg='u'
+        set  +$u_arg;
         source $final_path/bin/activate
-        set -u;
+        set  -$u_arg;
         pip3 install --upgrade setuptools wheel
         chown $synapse_user:root -R $final_path
         sudo -u $synapse_user env PATH=$PATH pip3 install --upgrade 'cryptography>=3.3'
@@ -59,8 +60,8 @@ install_sources() {
         pip3 install --upgrade 'Twisted>=20.3.0<21' matrix-synapse==$upstream_version matrix-synapse-ldap3
 
         # This function was defined when we called "source $final_path/bin/activate". With this function we undo what "$final_path/bin/activate" does
-        set +u;
+        set  +$u_arg;
         deactivate
-        set -u;
+        set  -$u_arg;
     fi
 }