diff --git a/Library/Homebrew/shims/mac/super/ruby b/Library/Homebrew/shims/mac/super/ruby
index 9a125dc7e2..3d85702eb9 100755
--- a/Library/Homebrew/shims/mac/super/ruby
+++ b/Library/Homebrew/shims/mac/super/ruby
@@ -3,13 +3,13 @@
 # System Ruby's mkmf on Mojave (10.14) and later require SDKROOT set to work correctly.
 
 # Don't need shellcheck to follow the `source`.
-# shellcheck disable=SC1090
-source "$HOMEBREW_LIBRARY/Homebrew/shims/utils.sh"
+# shellcheck disable=SC1090,SC2154
+source "${HOMEBREW_LIBRARY}/Homebrew/shims/utils.sh"
 
-try_exec_non_system "$SHIM_FILE" "$@"
+try_exec_non_system "${SHIM_FILE}" "$@"
 
-if [[ -z "$SDKROOT" && -n "$HOMEBREW_SDKROOT" ]]; then
-  export SDKROOT=$HOMEBREW_SDKROOT
+if [[ -z "${SDKROOT}" && -n "${HOMEBREW_SDKROOT}" ]]; then
+  export SDKROOT=${HOMEBREW_SDKROOT}
 fi
 
-safe_exec "/usr/bin/$SHIM_FILE" "$@"
+safe_exec "/usr/bin/${SHIM_FILE}" "$@"