diff --git a/scripts/apidoc/typedoc.ts b/scripts/apidoc/typedoc.ts
index 28a3db8545a..4a39bd3344a 100644
--- a/scripts/apidoc/typedoc.ts
+++ b/scripts/apidoc/typedoc.ts
@@ -154,7 +154,7 @@ export function extractModuleName(module: DeclarationReflection): string {
 
 export function extractModuleFieldName(module: DeclarationReflection): string {
   const moduleName = extractModuleName(module);
-  return moduleName.substring(0, 1).toLowerCase() + moduleName.substring(1);
+  return moduleName[0].toLowerCase() + moduleName.substring(1);
 }
 
 export const MISSING_DESCRIPTION = 'Missing';
diff --git a/src/modules/helpers/luhn-check.ts b/src/modules/helpers/luhn-check.ts
index ba68b41d470..42fbe1a5485 100644
--- a/src/modules/helpers/luhn-check.ts
+++ b/src/modules/helpers/luhn-check.ts
@@ -28,7 +28,7 @@ function luhnChecksum(str: string): number {
   let sum = 0;
   let alternate = false;
   for (let i = str.length - 1; i >= 0; i--) {
-    let n = Number.parseInt(str.substring(i, i + 1));
+    let n = Number.parseInt(str[i]);
     if (alternate) {
       n *= 2;
       if (n > 9) {