diff --git a/common/include/3d.h b/common/include/3d.h
index a85f04d49..d22eb0982 100644
--- a/common/include/3d.h
+++ b/common/include/3d.h
@@ -216,27 +216,4 @@ bool g3_draw_bitmap(vms_vector *pos,fix width,fix height,grs_bitmap *bm);
 //NULL for either or both restores defaults
 void g3_set_special_render(void (*tmap_drawer)(),void (*flat_drawer)(),int (*line_drawer)(fix, fix, fix, fix));
 
-#ifdef DXX_BUILD_DESCENT_I
-//Object functions:
-
-//gives the interpreter an array of points to use
-void g3_set_interp_points(g3s_point *pointlist);
-
-//calls the object interpreter to render an object.  The object renderer
-//is really a seperate pipeline. returns true if drew
-bool g3_draw_polygon_model(void *model_ptr,grs_bitmap **model_bitmaps,vms_angvec *anim_angles,g3s_lrgb light,fix *glow_values);
-
-//init code for bitmap models
-void g3_init_polygon_model(void *model_ptr);
-
-//alternate interpreter for morphing object
-bool g3_draw_morphing_model(void *model_ptr,grs_bitmap **model_bitmaps,vms_angvec *anim_angles,g3s_lrgb light,vms_vector *new_points);
-
-// check a polymodel for it's color and return it
-int g3_poly_get_color(void *model_ptr);
-
-// routine to convert little to big endian in polygon model data
-void swap_polygon_model_data(ubyte *data);
-#endif
-
 #endif
diff --git a/d2x-rebirth/include/interp.h b/common/include/interp.h
similarity index 100%
rename from d2x-rebirth/include/interp.h
rename to common/include/interp.h
diff --git a/d1x-rebirth/main/lighting.c b/d1x-rebirth/main/lighting.c
index 6cbbb377c..83c57230a 100644
--- a/d1x-rebirth/main/lighting.c
+++ b/d1x-rebirth/main/lighting.c
@@ -31,6 +31,7 @@ COPYRIGHT 1993-1999 PARALLAX SOFTWARE CORPORATION.  ALL RIGHTS RESERVED.
 #include "vclip.h"
 #include "lighting.h"
 #include "3d.h"
+#include "interp.h"
 #include "laser.h"
 #include "timer.h"
 #include "player.h"
diff --git a/d1x-rebirth/main/morph.c b/d1x-rebirth/main/morph.c
index 297b0373f..06df3dce1 100644
--- a/d1x-rebirth/main/morph.c
+++ b/d1x-rebirth/main/morph.c
@@ -31,6 +31,7 @@ COPYRIGHT 1993-1998 PARALLAX SOFTWARE CORPORATION.  ALL RIGHTS RESERVED.
 #include "newdemo.h"
 #include "piggy.h"
 #include "bm.h"
+#include "interp.h"
 
 morph_data morph_objects[MAX_MORPH_OBJECTS];
 
diff --git a/d1x-rebirth/main/polyobj.c b/d1x-rebirth/main/polyobj.c
index e792d468b..16f8da90e 100644
--- a/d1x-rebirth/main/polyobj.c
+++ b/d1x-rebirth/main/polyobj.c
@@ -29,7 +29,7 @@ COPYRIGHT 1993-1998 PARALLAX SOFTWARE CORPORATION.  ALL RIGHTS RESERVED.
 #endif
 #include "polyobj.h"
 #include "vecmat.h"
-#include "3d.h"
+#include "interp.h"
 #include "dxxerror.h"
 #include "u_mem.h"
 #include "args.h"