diff --git a/docs/api.rst b/docs/api.rst
index 58661f157..6576e9edc 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -510,6 +510,7 @@ Functions
 ^^^^^^^^^
 .. doxygenfunction:: z_open
 .. doxygenfunction:: z_close
+.. doxygenfunction:: z_session_is_closed
 
 .. doxygenfunction:: z_session_loan
 .. doxygenfunction:: z_session_loan_mut