diff --git a/scheme/meep-ctl-swig.hpp b/scheme/meep-ctl-swig.hpp
index ac1c70ddc..5b90aad66 100644
--- a/scheme/meep-ctl-swig.hpp
+++ b/scheme/meep-ctl-swig.hpp
@@ -57,7 +57,7 @@ ctlio::cnumber_list make_casimir_g_kz(double T, double dt, double sigma, meep::f
 
 ctlio::integer_list GDSII_layers(const char *fname);
 meep::volume GDSII_vol(const char *fname, int layer = -1, double zmin = 0, double zmax = 0);
-ctlio::simple_prism_list get_GDSII_prisms(const char *GDSIIFile, int Layer = -1, double zmin = 0.0, double zmax = 0.0);
+SCM get_GDSII_prism_data(const char *GDSIIFile, int Layer = -1, double zmin = 0.0, double zmax = 0.0);
 
 // wrapper around constructor to fool SWIG
 meep::volume_list *make_volume_list(const meep::volume &v, int c, std::complex<double> weight,
diff --git a/scheme/meep.cpp b/scheme/meep.cpp
index 5cd225cd1..7dcee09de 100644
--- a/scheme/meep.cpp
+++ b/scheme/meep.cpp
@@ -214,19 +214,24 @@ volume GDSII_vol(const char *fname, int layer, double zmin, double zmax) {
   return meep_geom::get_GDSII_volume(fname, layer, zmin, zmax);
 }
 
-ctlio::simple_prism_list get_GDSII_prisms(const char *GDSIIFile, int Layer, double zmin, double zmax) {
+/* We have to jump through some hoops here because the geometric_object data type used
+   in meepgeom (from libctlgeom) is different from the generated ctlio::geometric_object.
+   So we take the list of prisms from meep_geom::get_GDSII_prisms and return a simple
+   Scheme list of triples (vertices height axis).  meep.scm then defines a higher-level
+   function get-GDSII-prisms that constructs the actual prism objects again */
+SCM get_GDSII_prism_data(const char *GDSIIFile, int Layer, double zmin, double zmax) {
   geometric_object_list go = meep_geom::get_GDSII_prisms(NULL, GDSIIFile, Layer, zmin, zmax);
-  ctlio::simple_prism_list res;
-  res.num_items = go.num_items;
-  res.items = new ctlio::simple_prism[res.num_items];
-  for (int i = 0; i < res.num_items; ++i) {
+  SCM res = SCM_EOL;
+  for (int i = go.num_items - 1; i >= 0; --i) {
     prism *p = go.items[i].subclass.prism_data;
-    res.items[i].vertices.num_items = p->vertices.num_items;
-    res.items[i].vertices.items = p->vertices.items;
-    res.items[i].height = p->height;
-    res.items[i].axis = p->axis;
+    res = scm_cons(scm_list_3(ctl_convert_list_to_scm(make_vector3_list(p->vertices.num_items, p->vertices.items)),
+                              ctl_convert_number_to_scm(p->height),
+                              ctl_convert_vector3_to_scm(p->axis)),
+                   res);
+    free(p->vertices.items);
+    // fixme: free the rest of the prism data
     free(p);
   }
   delete[] go.items;
   return res;
-}
\ No newline at end of file
+}
diff --git a/scheme/meep.scm.in b/scheme/meep.scm.in
index f08ed6da8..01233005c 100644
--- a/scheme/meep.scm.in
+++ b/scheme/meep.scm.in
@@ -1122,12 +1122,10 @@
 
 (export-type (make-list-type 'integer))
 
-(define-class simple-prism no-parent
-  (define-property vertices no-default (make-list-type 'vector3))
-  (define-property height no-default 'number)
-  (define-property axis no-default 'vector3))
-(export-type (make-list-type 'simple-prism))
-
+(define* (get-GDSII-prisms m GDSIIFile #:optional (layer -1) (zmin 0) (zmax 0))
+  (map (lambda (data)
+        (make prism (material m) (center auto-center) (vertices (car data)) (height (cadr data)) (axis (caddr data))))
+       (get-GDSII-prism-data GDSIIFile layer zmin zmax)))
 
 ; ****************************************************************
 ; harminv functions for extracting bands, etcetera