diff --git a/scripts/install b/scripts/install
index f7adc9b..f227bdb 100644
--- a/scripts/install
+++ b/scripts/install
@@ -141,7 +141,7 @@ else
     test -e $final_path/bin || virtualenv -p python2.7 $final_path
 
     # Install synapse in virtualenv
-    PS1=""
+    PS1=${PS1:-}
     cp ../conf/virtualenv_activate $final_path/bin/activate
     ynh_replace_string __FINAL_PATH__ $final_path $final_path/bin/activate
 
@@ -168,6 +168,7 @@ fi
 #=================================================
 
 # Go in virtualenvironnement
+PS1=${PS1:-}
 source $final_path/bin/activate
 
 # Get the dh.pem if exist
diff --git a/scripts/upgrade b/scripts/upgrade
index 4d9b53b..deede78 100644
--- a/scripts/upgrade
+++ b/scripts/upgrade
@@ -91,7 +91,7 @@ else
     test -e $final_path/bin || virtualenv -p python2.7 $final_path
 
     # Install synapse in virtualenv
-    PS1=""
+    PS1=${PS1:-}
     cp ../conf/virtualenv_activate $final_path/bin/activate
     ynh_replace_string __FINAL_PATH__ $final_path $final_path/bin/activate
 
@@ -120,6 +120,7 @@ fi
 if [[ -z "$registration_shared_secret" ]]
 then
     # Go in virtualenvironnement
+    PS1=${PS1:-}
     source $final_path/bin/activate
 
     # Get the dh.pem if exist