diff --git a/common/modules/io.jsm b/common/modules/io.jsm
index 84b7984e..9c23de28 100644
--- a/common/modules/io.jsm
+++ b/common/modules/io.jsm
@@ -238,7 +238,13 @@ var IO = Module("io", {
     },
 
     validateCharset: function validateCharset(charset) {
-        new TextDecoder(charset);
+        try {
+            new TextDecoder(charset);
+            return true;
+        }
+        catch (e) {
+            return false;
+        }
     },
 
     // TODO: there seems to be no way, short of a new component, to change