diff --git a/sumpy/kernel.py b/sumpy/kernel.py
index d88ec3d6a44088646a73192227ab4a523095c0e7..d4c45a4b6317bdf006ff1f46c771330c12faf422 100644
--- a/sumpy/kernel.py
+++ b/sumpy/kernel.py
@@ -238,7 +238,7 @@ class Kernel:
 
         The typical use of this function is to apply target-variable
         derivatives to the kernel.
-        
+
         :arg expr: may be a :class:`sympy.Expr` or a
             :class:`sumpy.tools.DifferentiatedExprDerivativeTaker`.
         """