diff --git a/lib/linter.sh b/lib/linter.sh
index a6fb1a02..cb271265 100755
--- a/lib/linter.sh
+++ b/lib/linter.sh
@@ -64,12 +64,20 @@ source /action/lib/functions/worker.sh # Source the function script(s)
 ###########
 # GLOBALS #
 ###########
+# GitHub API root url
+if [ -n "$GITHUB_CUSTOM_API_URL" ]; then
+  GITHUB_API_URL="${GITHUB_CUSTOM_API_URL}"
+elif [ -z "$GITHUB_API_URL" ]; then
+  GITHUB_API_URL="https://api.github.com"
+fi
+# Remove trailing slash if present
+GITHUB_API_URL="${GITHUB_API_URL%/}"
+
 # Default Vars
-DEFAULT_RULES_LOCATION='/action/lib/.automation'                    # Default rules files location
-LINTER_RULES_PATH="${LINTER_RULES_PATH:-.github/linters}"           # Linter rules directory
-GITHUB_API_URL="${GITHUB_CUSTOM_API_URL:-"https://api.github.com"}" # GitHub API root url
-VERSION_FILE='/action/lib/functions/linterVersions.txt'             # File to store linter versions
-export VERSION_FILE                                                 # Workaround SC2034
+DEFAULT_RULES_LOCATION='/action/lib/.automation'          # Default rules files location
+LINTER_RULES_PATH="${LINTER_RULES_PATH:-.github/linters}" # Linter rules directory
+VERSION_FILE='/action/lib/functions/linterVersions.txt'   # File to store linter versions
+export VERSION_FILE                                       # Workaround SC2034
 
 ###############
 # Rules files #