diff --git a/GIFEncoder.js b/GIFEncoder.js
index dbd13e0..8fa6278 100755
--- a/GIFEncoder.js
+++ b/GIFEncoder.js
@@ -341,7 +341,7 @@ const GIFEncoder = function() {
 			var dg = g - (colorTab[i++] & 0xff);
 			var db = b - (colorTab[i] & 0xff);
 			var d = dr * dr + dg * dg + db * db;
-			var index = i / 3;
+			var index = i / 3 | 0;
 			if (usedEntry[index] && (d < dmin)) {
 				dmin = d;
 				minpos = index;