diff --git a/doc/uImage.FIT/source_file_format.txt b/doc/uImage.FIT/source_file_format.txt
index 3db068d..9c527c3 100644
--- a/doc/uImage.FIT/source_file_format.txt
+++ b/doc/uImage.FIT/source_file_format.txt
@@ -56,7 +56,7 @@
 conforms to bindings defined in this document.
 
 .its	- image tree source
-.fit	- flattened image tree blob
+.itb	- flattened image tree blob
 
 c) Image building procedure