diff --git a/xlsx.js b/xlsx.js
index c29f5ce..1f9ac9d 100644
--- a/xlsx.js
+++ b/xlsx.js
@@ -1314,8 +1314,14 @@ function getdata(data) {
 
 function safegetzipfile(zip, file) {
 	var f = file; if(zip.files[f]) return zip.files[f];
-	f = file.toLowerCase(); if(zip.files[f]) return zip.files[f];
-	f = f.replace(/\//g,'\\'); if(zip.files[f]) return zip.files[f];
+
+	var lowerCaseFiles = {};
+	for (var key in zip.files) {
+		lowerCaseFiles[key.toLowerCase()] = zip.files[key];
+	}
+
+	f = file.toLowerCase(); if(lowerCaseFiles[f]) return lowerCaseFiles[f];
+	f = f.replace(/\//g,'\\'); if(lowerCaseFiles[f]) return lowerCaseFiles[f];
 	return null;
 }