diff --git a/src/libcosimpy/CosimExecution.py b/src/libcosimpy/CosimExecution.py
index 13f72a5..9f01637 100644
--- a/src/libcosimpy/CosimExecution.py
+++ b/src/libcosimpy/CosimExecution.py
@@ -60,7 +60,7 @@ def __init__(self, create_key: object = None, execution_ptr: Optional[CosimExecu
             lib=CosimLibrary.lib,
             funcname="cosim_execution_step",
             argtypes=[POINTER(CosimExecution), c_int64],
-            restype=None,
+            restype=c_int,
         )
         self.__add_local_slave = wrap_function(
             lib=CosimLibrary.lib,