diff --git a/gmatch4py/kernels/weisfeiler_lehman.pyx b/gmatch4py/kernels/weisfeiler_lehman.pyx
index 784d50263180885b06fd29f001f6db6f6929a36f..93a78cbbc36b49d0f328198fa7f38a59ea1fa22a 100644
--- a/gmatch4py/kernels/weisfeiler_lehman.pyx
+++ b/gmatch4py/kernels/weisfeiler_lehman.pyx
@@ -142,4 +142,4 @@ cdef class WeisfeleirLehmanKernel(Base):
             k += np.dot(phi.transpose(), phi)
             it = it + 1
 
-        return minmax_scale(k).todense()
\ No newline at end of file
+        return np.ma.getdata(minmax_scale(k))
\ No newline at end of file