diff --git a/debian/config.exs b/debian/config.exs.tpl
similarity index 100%
rename from debian/config.exs
rename to debian/config.exs.tpl
diff --git a/debian/install b/debian/install
index 7ec3dce8..175bcb9e 100644
--- a/debian/install
+++ b/debian/install
@@ -1,2 +1,2 @@
-debian/config.exs etc/mobilizon
+debian/config.exs.tpl etc/mobilizon
 _build/prod/rel/mobilizon usr/share
diff --git a/debian/postinst b/debian/postinst
index ddf8228e..2431f0ca 100644
--- a/debian/postinst
+++ b/debian/postinst
@@ -10,7 +10,7 @@ set -e
 
 case "$1" in
     configure)
-        # TODO create system user
+        # Create a dedicated system user
         if ! getent passwd mobilizon >/dev/null; then
             adduser \
               --disabled-password \
@@ -23,24 +23,30 @@ case "$1" in
               mobilizon
         fi
 
-        # Use debconf values to initialize config.exs
-        db_get mobilizon/domain_name
-        sed -i "s/__DOMAIN_NAME__/${RET}/" /etc/mobilizon/config.exs
+        if [ ! -f /etc/mobilizon/config.exs ]; then
+            # Use debconf values to initialize config.exs
+            cp /etc/mobilizon/config.exs.tpl /etc/mobilizon/config.exs.tmp
 
-        db_get mobilizon/listen_port
-        sed -i "s/__LISTEN_PORT__/${RET}/" /etc/mobilizon/config.exs
+            db_get mobilizon/domain_name
+            sed -i "s/__DOMAIN_NAME__/${RET}/" /etc/mobilizon/config.exs.tmp
 
-        db_get mobilizon/db_host
-        sed -i "s/__DB_HOST__/${RET}/" /etc/mobilizon/config.exs
+            db_get mobilizon/listen_port
+            sed -i "s/__LISTEN_PORT__/${RET}/" /etc/mobilizon/config.exs.tmp
 
-        db_get mobilizon/db_name
-        sed -i "s/__DB_NAME__/${RET}/" /etc/mobilizon/config.exs
+            db_get mobilizon/db_host
+            sed -i "s/__DB_HOST__/${RET}/" /etc/mobilizon/config.exs.tmp
 
-        db_get mobilizon/db_username
-        sed -i "s/__DB_USERNAME__/${RET}/" /etc/mobilizon/config.exs
+            db_get mobilizon/db_name
+            sed -i "s/__DB_NAME__/${RET}/" /etc/mobilizon/config.exs.tmp
 
-        db_get mobilizon/db_userpass
-        sed -i "s/__DB_USERPASS__/${RET}/" /etc/mobilizon/config.exs
+            db_get mobilizon/db_username
+            sed -i "s/__DB_USERNAME__/${RET}/" /etc/mobilizon/config.exs.tmp
+
+            db_get mobilizon/db_userpass
+            sed -i "s/__DB_USERPASS__/${RET}/" /etc/mobilizon/config.exs.tmp
+
+            mv /etc/mobilizon/config.exs.tmp /etc/mobilizon/config.exs
+        fi
 
     ;;