diff --git a/scripts/_common.sh b/scripts/_common.sh
index e5b02a2..54f3ad5 100644
--- a/scripts/_common.sh
+++ b/scripts/_common.sh
@@ -16,3 +16,46 @@ exec_as() {
     sudo -u "$USER" "$@"
   fi
 }
+
+# Execute a command with Composer
+#
+# usage: ynh_composer_exec [--workdir=$final_path] --commands="commands"
+# | arg: -w, --workdir - The directory from where the command will be executed. Default $final_path.
+# | arg: -c, --commands - Commands to execute.
+ynh_composer_exec () {
+	# Declare an array to define the options of this helper.
+	local legacy_args=wc
+	declare -Ar args_array=( [w]=workdir= [c]=commands= )
+	local workdir
+	local commands
+	# Manage arguments with getopts
+	ynh_handle_getopts_args "$@"
+	workdir="${workdir:-$final_path}"
+
+	COMPOSER_HOME="$workdir/.composer" \
+		php "$workdir/composer.phar" $commands \
+		-d "$workdir" --quiet --no-interaction
+}
+
+# Install and initialize Composer in the given directory
+#
+# usage: ynh_install_composer [--workdir=$final_path]
+# | arg: -w, --workdir - The directory from where the command will be executed. Default $final_path.
+ynh_install_composer () {
+	# Declare an array to define the options of this helper.
+	local legacy_args=w
+	declare -Ar args_array=( [w]=workdir= )
+	local workdir
+	# Manage arguments with getopts
+	ynh_handle_getopts_args "$@"
+	workdir="${workdir:-$final_path}"
+
+	curl -sS https://getcomposer.org/installer \
+		| COMPOSER_HOME="$workdir/.composer" \
+		php -- --quiet --install-dir="$workdir" \
+		|| ynh_die "Unable to install Composer."
+
+	# update dependencies to create composer.lock
+	ynh_composer_exec --workdir="$workdir" --commands="install --no-dev" \
+		|| ynh_die "Unable to update core dependencies with Composer."
+}
diff --git a/scripts/install b/scripts/install
index 3e26d0c..084ec89 100644
--- a/scripts/install
+++ b/scripts/install
@@ -146,22 +146,10 @@ touch "$final_path/admin/stdout.log"
 #=================================================
 ynh_print_info "Initializing database..."
 
-# Set permissions for initialization
-chown -R $app: "$final_path"
-
 # Install composer
-curl -sS https://getcomposer.org/installer \
-	| COMPOSER_HOME="$final_path/.composer" \
-	php -- --quiet --install-dir="$final_path" \
-	|| ynh_die "Unable to install Composer"
+ynh_install_composer
 
-# Update dependencies to create composer.lock
-exec_as $app COMPOSER_HOME="$final_path/.composer" \
-	php "$final_path/composer.phar" install --no-dev \
-	-d "$final_path" --quiet --no-interaction \
-	|| ynh_die "Unable to update core dependencies with Composer"
-
-ynh_exec_warn_less exec_as $app php "$final_path/admin/migration.php"
+ynh_exec_warn_less php "$final_path/admin/migration.php"
 
 #=================================================
 # GENERIC FINALIZATION
diff --git a/scripts/upgrade b/scripts/upgrade
index 030ec26..331e3e8 100644
--- a/scripts/upgrade
+++ b/scripts/upgrade
@@ -178,22 +178,10 @@ touch "$final_path/admin/stdout.log"
 #=================================================
 ynh_print_info "Upgrading database..."
 
-# Set permissions for initilization
-chown -R $app: "$final_path"
-
 # Install composer
-curl -sS https://getcomposer.org/installer \
-	| COMPOSER_HOME="$final_path/.composer" \
-	php -- --quiet --install-dir="$final_path" \
-	|| ynh_die "Unable to install Composer"
+ynh_install_composer
 
-# Update dependencies to create composer.lock
-exec_as $app COMPOSER_HOME="$final_path/.composer" \
-	php "$final_path/composer.phar" install --no-dev \
-	-d "$final_path" --quiet --no-interaction \
-	|| ynh_die "Unable to update core dependencies with Composer"
-
-ynh_exec_warn_less exec_as $app php "$final_path/admin/migration.php"
+ynh_exec_warn_less php "$final_path/admin/migration.php"
 
 #=================================================
 # GENERIC FINALIZATION