diff --git a/lib/self-upgrade.bash b/lib/self-upgrade.bash
index f1ad863..f52ca36 100755
--- a/lib/self-upgrade.bash
+++ b/lib/self-upgrade.bash
@@ -1,15 +1,15 @@
 #!/usr/bin/env miaou-bash
 
 # CONSTANTS
-
-readonly MAIN_TAR_GZ_URL="https://git.artcode.re/miaou/miaou-bash/archive/main.tar.gz"
+[[ ! -v MAIN_TAR_GZ_URL ]] &&
+  readonly MAIN_TAR_GZ_URL="https://git.artcode.re/miaou/miaou-bash/archive/main.tar.gz"
 
 # FUNCTIONS
 
 function bootstrap {
   cd "$(mktemp -d)" || exit 3
   curl -s -O $MAIN_TAR_GZ_URL
-  tar -xzf main.tar.gz --directory "$(dirname $MIAOU_BASH_DIR)"
+  tar -xzf main.tar.gz --directory "$(dirname "$MIAOU_BASH_DIR")"
 
   local source_bin="$MIAOU_BASH_DIR/bin/miaou-bash"
   local dest_bin="/usr/bin/miaou-bash"