diff --git a/dist/index.js b/dist/index.js
index c6de35c..1d59e53 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -84,7 +84,21 @@ class ExchNumberFormat {
         };
         this.intlOptions = { ...defaultOptions, ...options };
         this.originalCurrency = this.intlOptions.currency;
-        let setLocale = locales === 'auto' ? (navigator.languages && navigator.languages.length ? navigator.languages[0] : navigator.language) : locales;
+        let setLocale;
+        if (locales === 'auto') {
+            if (typeof window !== 'undefined' && navigator.languages && navigator.languages.length) {
+                setLocale = navigator.languages[0];
+            }
+            else if (typeof window !== 'undefined' && navigator.language) {
+                setLocale = navigator.language;
+            }
+            else {
+                setLocale = 'en';
+            }
+        }
+        else {
+            setLocale = locales;
+        }
         if (this.originalCurrency && this.customCurrencyData[this.originalCurrency.toUpperCase()]) {
             const currencyData = this.customCurrencyData[this.originalCurrency.toUpperCase()];
             this.intlOptions.minimumFractionDigits = currencyData.defaultDecimals;
diff --git a/package.json b/package.json
index e3c69b4..d8d9c2f 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "exchange-rounding",
-  "version": "1.0.4",
+  "version": "1.0.5",
   "description": "Exchange Number Formatting",
   "main": "dist/index.js",
   "type": "module",
diff --git a/src/index.ts b/src/index.ts
index efdb794..af57dc8 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -102,7 +102,19 @@ class ExchNumberFormat {
 		this.originalCurrency = this.intlOptions.currency;
 
 		// Determine the locale
-		let setLocale = locales === 'auto' ? (navigator.languages && navigator.languages.length ? navigator.languages[0] : navigator.language) : locales;
+		let setLocale: string;
+		if (locales === 'auto') {
+			// Check if running in a browser environment
+			if (typeof window !== 'undefined' && navigator.languages && navigator.languages.length) {
+				setLocale = navigator.languages[0];
+			} else if (typeof window !== 'undefined' && navigator.language) {
+				setLocale = navigator.language;
+			} else {
+				setLocale = 'en'; // Default to 'en' or any other default locale
+			}
+		} else {
+			setLocale = locales;
+		}
 
 		if (this.originalCurrency && this.customCurrencyData[this.originalCurrency.toUpperCase()]) {
 			const currencyData = this.customCurrencyData[this.originalCurrency.toUpperCase()];
diff --git a/tsconfig.json b/tsconfig.json
index 9264567..cde644f 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -6,6 +6,7 @@
     "strict": true,
     "typeRoots": ["./node_modules/@types", "./types"],
     "removeComments": true,
+    "esModuleInterop": true,
     "declaration": true
   },
   "include": ["src/**/*.ts"],
diff --git a/tsconfig.test.json b/tsconfig.test.json
index 5ac4d30..d3774e7 100644
--- a/tsconfig.test.json
+++ b/tsconfig.test.json
@@ -2,6 +2,7 @@
   "extends": "./tsconfig.json",
   "compilerOptions": {
     "module": "Node16",
+    "esModuleInterop": true,
     "outDir": "./dist-test"
   },
   "include": ["src/**/*.ts", "test/**/*.ts"],