diff --git a/src/profile.sh b/src/profile.sh
index 3dbdeac..abbe12c 100644
--- a/src/profile.sh
+++ b/src/profile.sh
@@ -1,8 +1,11 @@
+#!/usr/bin/env sh
+
 # To avoid potential situation where cdm(1) crashes on every TTY, here we
 # default to execute cdm(1) on tty1 only, and leave other TTYs untouched.
-if [[ "$(tty)" == '/dev/tty1' ]]; then
-    [[ -n "$CDM_SPAWN" ]] && return
+if [ "$(tty)" = '/dev/tty1' ]; then
+    [ -n "$CDM_SPAWN" ] && return
     # Avoid executing cdm(1) when X11 has already been started.
-    [[ -z "$DISPLAY$SSH_TTY$(pgrep xinit)" ]] && exec cdm
+
+    [ -z "$DISPLAY$SSH_TTY$(pgrep xinit)" ] && exec cdm
 fi