diff --git a/doc/manual/source/the-model-file.rst b/doc/manual/source/the-model-file.rst
index 3d0cb1ba848e6cc55d70fb086f64545d0ec12c0d..cfd44369abc80e10d7b3d4ab977ee32974be82ec 100644
--- a/doc/manual/source/the-model-file.rst
+++ b/doc/manual/source/the-model-file.rst
@@ -2048,7 +2048,7 @@ 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.