diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9b0e53f..66fa39c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@
 ### 🐛Fixed
 - Error when checking the number of streamlines in the weighted LASSO function
 - Error in verifying voxel correspondence between the lesion mask passed through the dictionary and the ISO weights map
+- Error when checking the number of streamlines in the grouping structure for group LASSO regularization
 
 ---
 ---
diff --git a/commit/core.pyx b/commit/core.pyx
index e0754ed..8ec68e6 100644
--- a/commit/core.pyx
+++ b/commit/core.pyx
@@ -1115,7 +1115,7 @@ cdef class Evaluation :
         # check if group_idx contains all the indices of the input streamlines
         if regularisation['regIC'] == 'group_lasso' or regularisation['regIC'] == 'sparse_group_lasso':
             all_idx_in = np.sort(np.unique(np.concatenate(dictIC_params['group_idx'])))
-            all_idx = np.arange(self.DICTIONARY['IC']['nSTR'], dtype=np.int32)
+            all_idx = np.arange(self.DICTIONARY['TRK']['kept'].size, dtype=np.int32)
             if np.any(all_idx_in != all_idx):
                 logger.error('Group indices must contain all the indices of the input streamlines')