diff --git a/doc/manual/source/the-model-file.rst b/doc/manual/source/the-model-file.rst
index 653d83f128147cfea601e0cc67006ffe88e7569e..af3a37f45a814dce74a952767cc92da04bec31b7 100644
--- a/doc/manual/source/the-model-file.rst
+++ b/doc/manual/source/the-model-file.rst
@@ -2051,7 +2051,7 @@ in this case ``initval`` is used to specify the terminal conditions.
 
     .. option:: last_obs = {INTEGER | DATE}
 
-        The observaton number or the date (see
+        The observation number or the date (see
 	:ref:`dates-members`) of the last observation to be used in
 	the file.