diff --git a/chainopy/exceptions.py b/chainopy/exceptions.py
index 4f7d6ba..e5f2895 100644
--- a/chainopy/exceptions.py
+++ b/chainopy/exceptions.py
@@ -36,7 +36,7 @@ def wrapper(*args, **kwargs):
             elif func.__name__ == "simulate":
                 n_steps = args[2]
                 initial_state = args[1]
-                if not isinstance(n_steps, int) or len(n_steps) <= 0:
+                if not isinstance(n_steps, int) or n_steps <= 0:
                     raise ValueError("Argument 'n_steps' must be a non-empty string.")
 
                 if not isinstance(initial_state, str) or (