diff --git a/addons/document/models/ir_attachment.py b/addons/document/models/ir_attachment.py
index 7e1afe36e4e..2bc6aee234d 100644
--- a/addons/document/models/ir_attachment.py
+++ b/addons/document/models/ir_attachment.py
@@ -93,7 +93,7 @@ class IrAttachment(models.Model):
         '''Index PDF documents'''
 
         buf = u""
-        if bin_data.startswith('%PDF-'):
+        if bin_data.startswith(b'%PDF-'):
             f = io.BytesIO(bin_data)
             try:
                 pdf = PyPDF2.PdfFileReader(f, overwriteWarnings=False)