diff --git a/src/core.js b/src/core.js
index 4313959a8..ab2509016 100644
--- a/src/core.js
+++ b/src/core.js
@@ -7,7 +7,7 @@ var globalScope = (typeof window === 'undefined') ? this : window;
 
 var ERRORS = 0, WARNINGS = 1, TODOS = 5;
 var verbosity = WARNINGS;
-var useWorker = true;
+var useWorker = false;
 
 // The global PDFJS object exposes the API
 // In production, it will be declared outside a global wrapper