diff --git a/pdf.js b/pdf.js
index 814c99f75..48fa004e6 100644
--- a/pdf.js
+++ b/pdf.js
@@ -2971,6 +2971,7 @@ var Catalog = (function() {
 
 var PDFDoc = (function() {
     function constructor(stream) {
+        assertWellFormed(stream.length > 0, "stream must have data");
         this.stream = stream;
         this.setup();
     }
diff --git a/test/test.py b/test/test.py
index 367347e88..00b87f786 100644
--- a/test/test.py
+++ b/test/test.py
@@ -275,7 +275,7 @@ def downloadLinkedPDFs(manifestList):
             sys.stdout.flush()
             response = urllib2.urlopen(link)
 
-            with open(f, 'w') as out:
+            with open(f, 'wb') as out:
                 out.write(response.read())
 
             print 'done'