diff --git a/src/cjs/index.cjs b/src/cjs/index.cjs
index 0124347..07524c6 100644
--- a/src/cjs/index.cjs
+++ b/src/cjs/index.cjs
@@ -81,7 +81,7 @@ function base (ALPHABET) {
     const size = (((source.length - psz) * FACTOR) + 1) >>> 0 // log(58) / log(256), rounded up.
     const b256 = new Uint8Array(size)
     // Process the characters.
-    while (source[psz]) {
+    while (psz < source.length) {
       // Decode character
       let carry = BASE_MAP[source.charCodeAt(psz)]
       // Invalid character
diff --git a/src/esm/index.js b/src/esm/index.js
index ac60db8..ce48a14 100644
--- a/src/esm/index.js
+++ b/src/esm/index.js
@@ -79,7 +79,7 @@ function base (ALPHABET) {
     const size = (((source.length - psz) * FACTOR) + 1) >>> 0 // log(58) / log(256), rounded up.
     const b256 = new Uint8Array(size)
     // Process the characters.
-    while (source[psz]) {
+    while (psz < source.length) {
       // Decode character
       let carry = BASE_MAP[source.charCodeAt(psz)]
       // Invalid character
diff --git a/ts_src/index.ts b/ts_src/index.ts
index 66e0e4b..5f2431a 100644
--- a/ts_src/index.ts
+++ b/ts_src/index.ts
@@ -100,7 +100,7 @@ function base (ALPHABET: string): base.BaseConverter {
     const b256 = new Uint8Array(size)
 
     // Process the characters.
-    while (source[psz]) {
+    while (psz < source.length) {
       // Decode character
       let carry = BASE_MAP[source.charCodeAt(psz)]