diff --git a/common/main/gameseg.h b/common/main/gameseg.h
index 0e66418e3..9f2ccbe0a 100644
--- a/common/main/gameseg.h
+++ b/common/main/gameseg.h
@@ -111,7 +111,7 @@ int check_lsegments_validity(void);
 //      set to WID_FLY_FLAG to see if a robot could fly from one to the other.
 //      Search up to a maximum depth of max_depth.
 //      Return the distance.
-extern fix find_connected_distance(vms_vector *p0, int seg0, vms_vector *p1, int seg1, int max_depth, int wid_flag);
+fix find_connected_distance(const vms_vector *p0, int seg0, const vms_vector *p1, int seg1, int max_depth, int wid_flag);
 
 //create a matrix that describes the orientation of the given segment
 extern void extract_orient_from_segment(vms_matrix *m,segment *seg);
diff --git a/similar/main/digiobj.cpp b/similar/main/digiobj.cpp
index 8b31ddf5e..816be9215 100644
--- a/similar/main/digiobj.cpp
+++ b/similar/main/digiobj.cpp
@@ -122,8 +122,7 @@ static int digi_unxlat_sound(int soundno)
 	return 0;
 }
 
-
-static void digi_get_sound_loc( vms_matrix * listener, vms_vector * listener_pos, int listener_seg, vms_vector * sound_pos, int sound_seg, fix max_volume, int *volume, int *pan, fix max_distance )
+static void digi_get_sound_loc( const vms_matrix * listener, const vms_vector * listener_pos, int listener_seg, const vms_vector * sound_pos, int sound_seg, fix max_volume, int *volume, int *pan, fix max_distance )
 {
 
 	vms_vector	vector_to_sound;
diff --git a/similar/main/gameseg.cpp b/similar/main/gameseg.cpp
index 706616aa3..f7634e6c6 100644
--- a/similar/main/gameseg.cpp
+++ b/similar/main/gameseg.cpp
@@ -883,7 +883,7 @@ static void add_to_fcd_cache(int seg0, int seg1, int depth, fix dist)
 //	Determine whether seg0 and seg1 are reachable in a way that allows sound to pass.
 //	Search up to a maximum depth of max_depth.
 //	Return the distance.
-fix find_connected_distance(vms_vector *p0, int seg0, vms_vector *p1, int seg1, int max_depth, int wid_flag)
+fix find_connected_distance(const vms_vector *p0, int seg0, const vms_vector *p1, int seg1, int max_depth, int wid_flag)
 {
 	int		cur_seg;
 	int		sidenum;