diff --git a/src/felupe/assembly/expression/_basis.py b/src/felupe/assembly/expression/_basis.py
index 8667b76e..e72827b8 100644
--- a/src/felupe/assembly/expression/_basis.py
+++ b/src/felupe/assembly/expression/_basis.py
@@ -123,7 +123,7 @@ class BasisField:
 
     ..  math::
 
-        \text{grad}(\varphi)_{ai~jk~qc} = \delta_{ij}
+        \text{grad}(\varphi)_{ai~jK~qc} = \delta_{ij}
             \left( \frac{\partial h_a}{\partial X_K} \right)_{qc}
 
     Examples