diff --git a/src/neurostatslib/solver.py b/src/neurostatslib/solver.py
index 178c9770..05b043f5 100644
--- a/src/neurostatslib/solver.py
+++ b/src/neurostatslib/solver.py
@@ -541,7 +541,7 @@ class GroupLassoSolver(ProxGradientSolver):
     Attributes
     ----------
     mask : Union[jnp.ndarray, NDArray]
-        A mask array indicating groups of features for regularization.
+        A 2d mask array indicating groups of features for regularization.
         Each row represents a group of features.
         Each column corresponds to a feature, where a value of 1 indicates that the feature belongs
         to the group, and a value of 0 indicates it doesn't.