diff --git a/brut.apktool/apktool-lib/src/main/java/brut/androlib/res/decoder/ResFileDecoder.java b/brut.apktool/apktool-lib/src/main/java/brut/androlib/res/decoder/ResFileDecoder.java
index 271d5d08..69280a20 100644
--- a/brut.apktool/apktool-lib/src/main/java/brut/androlib/res/decoder/ResFileDecoder.java
+++ b/brut.apktool/apktool-lib/src/main/java/brut/androlib/res/decoder/ResFileDecoder.java
@@ -53,7 +53,7 @@ public class ResFileDecoder {
         if (extPos == -1) {
             outFileName = outResName;
         } else {
-            ext = inFileName.substring(extPos);
+            ext = inFileName.substring(extPos).toLowerCase();
             outFileName = outResName + ext;
         }