diff --git a/src/sleplet/_convolution_methods.py b/src/sleplet/_convolution_methods.py
index 0371dd55..ade3c164 100644
--- a/src/sleplet/_convolution_methods.py
+++ b/src/sleplet/_convolution_methods.py
@@ -16,4 +16,4 @@ def sifting_convolution(
         if len(g_coefficient.shape) < len(f_coefficient.shape)
         else g_coefficient
     )
-    return (f_coefficient.T[:n] * g_reshape.conj().T[:n]).T.astype(f_coefficient.dtype)
+    return (f_coefficient.T[:n] * g_reshape.conj().T[:n]).T  # type: ignore[return-value]