diff --git a/src/shared/util.js b/src/shared/util.js
index 201ca3e0f..9d0d297eb 100644
--- a/src/shared/util.js
+++ b/src/shared/util.js
@@ -342,6 +342,7 @@ var PasswordException = (function PasswordExceptionClosure() {
 
   return PasswordException;
 })();
+PDFJS.PasswordException = PasswordException;
 
 var UnknownErrorException = (function UnknownErrorExceptionClosure() {
   function UnknownErrorException(msg, details) {
@@ -355,6 +356,7 @@ var UnknownErrorException = (function UnknownErrorExceptionClosure() {
 
   return UnknownErrorException;
 })();
+PDFJS.UnknownErrorException = UnknownErrorException;
 
 var InvalidPDFException = (function InvalidPDFExceptionClosure() {
   function InvalidPDFException(msg) {
@@ -367,6 +369,7 @@ var InvalidPDFException = (function InvalidPDFExceptionClosure() {
 
   return InvalidPDFException;
 })();
+PDFJS.InvalidPDFException = InvalidPDFException;
 
 var MissingPDFException = (function MissingPDFExceptionClosure() {
   function MissingPDFException(msg) {
@@ -379,6 +382,7 @@ var MissingPDFException = (function MissingPDFExceptionClosure() {
 
   return MissingPDFException;
 })();
+PDFJS.MissingPDFException = MissingPDFException;
 
 var NotImplementedException = (function NotImplementedExceptionClosure() {
   function NotImplementedException(msg) {
diff --git a/web/viewer.js b/web/viewer.js
index 7574fef3d..d332a5e1a 100644
--- a/web/viewer.js
+++ b/web/viewer.js
@@ -673,15 +673,11 @@ var PDFView = {
         self.loading = false;
       },
       function getDocumentError(exception) {
-        var name, message;
-        if (exception) {
-          name = exception.name;
-          message = exception.message;
-        }
+        var message = exception && exception.message;
         var loadingErrorMessage = mozL10n.get('loading_error', null,
           'An error occurred while loading the PDF.');
 
-        if (name === 'InvalidPDFException') {
+        if (exception instanceof PDFJS.InvalidPDFException) {
           // change error message also for other builds
           loadingErrorMessage = mozL10n.get('invalid_file_error', null,
                                             'Invalid or corrupted PDF file.');
@@ -689,13 +685,10 @@ var PDFView = {
 //        window.alert(loadingErrorMessage);
 //        return window.close();
 //#endif
-        }
-
-        if (name === 'MissingPDFException') {
+        } else if (exception instanceof PDFJS.MissingPDFException) {
           // special message for missing PDF's
           loadingErrorMessage = mozL10n.get('missing_file_error', null,
                                             'Missing PDF file.');
-
 //#if B2G
 //        window.alert(loadingErrorMessage);
 //        return window.close();