diff --git a/qpms/cytmatrices.pyx b/qpms/cytmatrices.pyx
index 29c8d7c..63bbc14 100644
--- a/qpms/cytmatrices.pyx
+++ b/qpms/cytmatrices.pyx
@@ -244,6 +244,10 @@ cdef class TMatrixGenerator:
             self.holder = what
             self.g.function = qpms_tmatrix_generator_axialsym
             self.g.params = (<__AxialSymParams?>self.holder).rawpointer()
+        elif isinstance(what, CTMatrix):
+            self.holder = what
+            self.g.function = qpms_tmatrix_generator_constant
+            self.g.params = <void*>(<CTMatrix?>self.holder).rawpointer()
         # TODO INTERPOLATOR
         else:
             raise TypeError("Can't construct TMatrixGenerator from that")
diff --git a/qpms/qpms_cdefs.pxd b/qpms/qpms_cdefs.pxd
index 56ac441..7e9bcd7 100644
--- a/qpms/qpms_cdefs.pxd
+++ b/qpms/qpms_cdefs.pxd
@@ -408,6 +408,7 @@ cdef extern from "tmatrices.h":
     qpms_errno_t qpms_tmatrix_generator_axialsym(qpms_tmatrix_t *t, cdouble omega, const void *params)
     qpms_errno_t qpms_tmatrix_generator_interpolator(qpms_tmatrix_t *t, cdouble omega, const void *params)
     qpms_errno_t qpms_tmatrix_generator_sphere(qpms_tmatrix_t *t, cdouble omega, const void *params)
+    qpms_errno_t qpms_tmatrix_generator_constant(qpms_tmatrix_t *t, cdouble omega, const void *params)
     struct qpms_tmatrix_generator_sphere_param_t:
         qpms_epsmu_generator_t outside
         qpms_epsmu_generator_t inside