diff --git a/SC2219.md b/SC2219.md
index e3b14de..4b4c768 100644
--- a/SC2219.md
+++ b/SC2219.md
@@ -18,7 +18,7 @@ let a++
 
 The `(( .. ))` arithmetic compound command evaluates expressions in the same way as `let`, except it's not subject to glob expansion and therefore requires no additional quoting or escaping. 
 
-This warning only triggers in Bash/Ksh scripts. In Sh/Dash, neither `let` nor `(( .. ))` are defined, but can be simulated with `[ $(( expr )) -ne 0 ]` to retain exit code, or `: $(( expr ))` to ignore it.
+This warning only triggers in Bash/Ksh scripts. In Sh/Dash, neither `let` nor `(( .. ))` are defined, but can be simulated with `[ $(( expr )) -ne 0 ]` to retain exit code, or `: $(( expr ))` to ignore it. For portability, the `$(( expr ))` syntax is defined in POSIX standard.
 
 ### Exceptions: