diff --git a/scripts/upgrade b/scripts/upgrade
index abf33c7..1fed1d7 100644
--- a/scripts/upgrade
+++ b/scripts/upgrade
@@ -286,6 +286,11 @@ then
     # We get the last version of the synapse_port_db script because an old version could be buggy.
     cp ../sources/synapse_port_db /opt/yunohost/matrix-synapse/bin/synapse_port_db
 
+    # Fix "PS1: unbound variable" On ARM architecture
+    PS1=""
+    cp ../conf/virtualenv_activate $final_path/bin/activate
+    ynh_replace_string __FINAL_PATH__ $final_path $final_path/bin/activate
+
     # Migrate database (in virtualenv)
     source $final_path/bin/activate
     /opt/yunohost/matrix-synapse/bin/synapse_port_db --sqlite-database /var/lib/matrix-synapse/homeserver.db \