diff --git a/quantecon/kalman.py b/quantecon/kalman.py
index e97a2a4b8..3bbda1406 100644
--- a/quantecon/kalman.py
+++ b/quantecon/kalman.py
@@ -13,7 +13,7 @@
 from .matrix_eqn import solve_discrete_riccati
 
 class Kalman:
-    r"""
+    """
     Implements the Kalman filter for the Gaussian state space model
 
     .. math::