diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index fe9399a8..a231d2e2 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -7,6 +7,15 @@
 Changelog
 =========
 
+
+4.1.4 - 2025-11-12
+------------------
+
+**Bug fix:**
+
+- Fixed :meth:`CategoricalMatrix.transpose_matvec` to operate on read-only buffers as well.
+
+
 4.1.3 - 2025-10-14
 ------------------
 
diff --git a/src/tabmat/ext/cat_split_helpers-tmpl.cpp b/src/tabmat/ext/cat_split_helpers-tmpl.cpp
index df7a21c6..af5793cc 100644
--- a/src/tabmat/ext/cat_split_helpers-tmpl.cpp
+++ b/src/tabmat/ext/cat_split_helpers-tmpl.cpp
@@ -5,7 +5,7 @@
 template <typename Int, typename F>
 void _transpose_matvec_${type}(
     Int n_rows,
-    Int* indices,
+    const Int* indices,
     F* other,
     F* res,
     Int res_size
diff --git a/src/tabmat/ext/categorical.pyx b/src/tabmat/ext/categorical.pyx
index be97844b..5852fc0e 100644
--- a/src/tabmat/ext/categorical.pyx
+++ b/src/tabmat/ext/categorical.pyx
@@ -16,12 +16,12 @@ ctypedef fused win_numeric:
     long long
 
 cdef extern from "cat_split_helpers.cpp":
-    void _transpose_matvec_all_rows_fast[Int, F](Int, Int*, F*, F*, Int)
-    void _transpose_matvec_all_rows_complex[Int, F](Int, Int*, F*, F*, Int, bool)
+    void _transpose_matvec_all_rows_fast[Int, F](Int, const int*, F*, F*, Int)
+    void _transpose_matvec_all_rows_complex[Int, F](Int, const int*, F*, F*, Int, bool)
 
 
 def transpose_matvec_fast(
-    int[:] indices,
+    const int[:] indices,
     floating[:] other,
     int n_cols,
     dtype,
@@ -68,7 +68,7 @@ def transpose_matvec_fast(
 
 
 def transpose_matvec_complex(
-    int[:] indices,
+    const int[:] indices,
     floating[:] other,
     int n_cols,
     dtype,
diff --git a/tests/test_transpose_matvec.py b/tests/test_transpose_matvec.py
new file mode 100644
index 00000000..ef8b3b06
--- /dev/null
+++ b/tests/test_transpose_matvec.py
@@ -0,0 +1,24 @@
+import narwhals as nw
+import numpy as np
+import pandas as pd
+
+import tabmat as tm
+
+
+def test_transpose_matvec_does_not_crash():
+    # With high n_categories CategoricalMatrix.indices is read-only.
+    # As a result, transpose_matvec method crashed with "buffer
+    # source array is read-only".
+
+    n = 797_586
+    n_categories = 58_059
+    categories = [f"cat[{i}]" for i in range(n_categories)]
+    indices = np.linspace(0, n_categories - 1, n).round().astype(int)
+    cat_vec = pd.Series(pd.Categorical.from_codes(indices, categories=categories))
+    cat_vec_nw = nw.from_native(cat_vec, allow_series=True)
+    weights = np.ones(n)
+    cat_matrix_tm = tm.CategoricalMatrix(cat_vec_nw)
+
+    result = cat_matrix_tm.transpose_matvec(weights)
+
+    assert result is not None