diff --git a/README.md b/README.md
index 250f8ec..8d19dde 100644
--- a/README.md
+++ b/README.md
@@ -29,7 +29,7 @@ c & A \\
 \quad\text{(Butcher table)}
 $$
 
-and many different **lower-triangular** approximation of the $Q$ matrix, named $Q_\Delta$,
+and many different **lower-triangular** approximations of the $Q$ matrix, named $Q_\Delta$,
 which are key elements for Spectral Deferred Correction (SDC), or more general Iterated Runge-Kutta Methods.
 
 [![DOI](https://zenodo.org/badge/804826743.svg)](https://zenodo.org/doi/10.5281/zenodo.11956478)
diff --git a/docs/index.rst b/docs/index.rst
index 0affdea..ececf84 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -42,7 +42,7 @@ It allows to generate :math:`Q`-coefficients for multi-stages methods (equivalen
     \end{array}
     \quad\text{(Butcher table)}
 
-and many different **lower-triangular** approximation of the :math:`Q` matrix, named :math:`Q_\Delta`,
+and many different **lower-triangular** approximations of the :math:`Q` matrix, named :math:`Q_\Delta`,
 which are key elements for Spectral Deferred Correction (SDC), or more general Iterated Runge-Kutta Methods.
 
 .. raw:: html