diff --git a/common/include/interp.h b/common/include/interp.h
index 396562aff..d8400da8a 100644
--- a/common/include/interp.h
+++ b/common/include/interp.h
@@ -16,12 +16,16 @@
 #include "dxxsconf.h"
 #include "compiler-array.h"
 
+#if defined(DXX_BUILD_DESCENT_I) || defined(DXX_BUILD_DESCENT_II)
 #if defined(DXX_BUILD_DESCENT_I)
 static const size_t glow_array_size = 1;
 #elif defined(DXX_BUILD_DESCENT_II)
 static const size_t glow_array_size = 2;
 #endif
 struct glow_values_t : public array<fix, glow_array_size> {};
+#else
+struct glow_values_t;
+#endif
 
 //Object functions:
 
diff --git a/common/main/ai.h b/common/main/ai.h
index 7d47bfc88..b23ccc319 100644
--- a/common/main/ai.h
+++ b/common/main/ai.h
@@ -33,6 +33,8 @@ COPYRIGHT 1993-1999 PARALLAX SOFTWARE CORPORATION.  ALL RIGHTS RESERVED.
 
 #ifdef __cplusplus
 
+struct point_seg;
+
 #define PLAYER_AWARENESS_INITIAL_TIME   (3*F1_0)
 #define MAX_PATH_LENGTH                 30          // Maximum length of path in ai path following.
 #define MAX_DEPTH_TO_SEARCH_FOR_PLAYER  10
@@ -44,6 +46,7 @@ COPYRIGHT 1993-1999 PARALLAX SOFTWARE CORPORATION.  ALL RIGHTS RESERVED.
 
 #define ROBOT_FIRE_AGITATION 94
 
+#if defined(DXX_BUILD_DESCENT_I) || defined(DXX_BUILD_DESCENT_II)
 #if defined(DXX_BUILD_DESCENT_I)
 extern	int	Boss_hit_this_frame;
 #elif defined(DXX_BUILD_DESCENT_II)
@@ -69,6 +72,9 @@ extern int Believed_player_seg;
 extern int Ai_last_missile_camera;
 #endif
 
+extern void create_awareness_event(object *objp, enum player_awareness_type_t type);         // object *objp can create awareness of player, amount based on "type"
+#endif
+
 struct boss_special_segment_array_t : public count_array_t<short, MAX_BOSS_TELEPORT_SEGS> {};
 struct boss_teleport_segment_array_t : public boss_special_segment_array_t {};
 struct boss_gate_segment_array_t : public boss_special_segment_array_t {};
@@ -90,7 +96,6 @@ extern void ai_move_one(object *objp);
 extern void do_ai_frame(object *objp);
 extern void init_ai_object(int objnum, int initial_mode, int hide_segment);
 extern void update_player_awareness(object *objp, fix new_awareness);
-extern void create_awareness_event(object *objp, enum player_awareness_type_t type);         // object *objp can create awareness of player, amount based on "type"
 extern void do_ai_frame_all(void);
 extern void reset_ai_states(object *objp);
 extern int create_path_points(object *objp, int start_seg, int end_seg, point_seg *point_segs, short *num_points, int max_depth, int random_flag, int safety_flag, int avoid_seg);
@@ -264,8 +269,10 @@ void buddy_message(const char * format, ... ) __attribute_format_printf(1, 2);
 extern void special_reactor_stuff(void);
 #endif
 
+#if defined(DXX_BUILD_DESCENT_I) || defined(DXX_BUILD_DESCENT_II)
 extern ai_local         Ai_local_info[MAX_OBJECTS];
 extern point_seg        Point_segs[MAX_POINT_SEGS];
+#endif
 extern point_seg        *Point_segs_free_ptr;
 
 extern int ai_save_state(PHYSFS_file * fp);
diff --git a/common/main/aistruct.h b/common/main/aistruct.h
index 11be14f52..8d6cc5142 100644
--- a/common/main/aistruct.h
+++ b/common/main/aistruct.h
@@ -306,10 +306,10 @@ typedef struct {
 } ai_cloak_info_rw;
 #endif
 
-typedef struct {
+struct point_seg {
 	int         segnum;
 	vms_vector  point;
-} point_seg;
+};
 
 typedef struct {
 	short       start, end;
diff --git a/common/main/bm.h b/common/main/bm.h
index 60d989906..5bc700fa3 100644
--- a/common/main/bm.h
+++ b/common/main/bm.h
@@ -41,6 +41,7 @@ COPYRIGHT 1993-1999 PARALLAX SOFTWARE CORPORATION.  ALL RIGHTS RESERVED.
 #define TMI_GOAL_HOARD  32  //this is used to remap the goals
 #endif
 
+#if defined(DXX_BUILD_DESCENT_I) || defined(DXX_BUILD_DESCENT_II)
 #if defined(DXX_BUILD_DESCENT_I)
 typedef struct {
 	char			filename[13];
@@ -127,6 +128,7 @@ extern bitmap_index ObjBitmaps[MAX_OBJ_BITMAPS];
 extern ushort ObjBitmapPtrs[MAX_OBJ_BITMAPS];
 extern int First_multi_bitmap_num;
 void compute_average_rgb(grs_bitmap *bm, fix *rgb);
+#endif
 
 // Initializes all bitmaps from BITMAPS.TBL file.
 int gamedata_read_tbl(int pc_shareware);
diff --git a/common/main/cntrlcen.h b/common/main/cntrlcen.h
index 30dde682d..2f1f795f8 100644
--- a/common/main/cntrlcen.h
+++ b/common/main/cntrlcen.h
@@ -94,6 +94,8 @@ static inline reactor *get_reactor_definition(int id)
 	return &Reactors[id];
 #endif
 }
+#else
+struct reactor;
 #endif
 
 //@@extern int N_controlcen_guns;
diff --git a/common/main/effects.h b/common/main/effects.h
index 24340588b..824ffaf0c 100644
--- a/common/main/effects.h
+++ b/common/main/effects.h
@@ -59,8 +59,10 @@ typedef struct eclip {
 	int     segnum,sidenum; //what seg & side, for one-shot clips
 } __pack__ eclip;
 
+#if defined(DXX_BUILD_DESCENT_I) || defined(DXX_BUILD_DESCENT_II)
 extern int Num_effects;
 extern eclip Effects[MAX_EFFECTS];
+#endif
 
 // Set up special effects.
 extern void init_special_effects();
diff --git a/common/main/fuelcen.h b/common/main/fuelcen.h
index 4d6cd099e..1c5cca139 100644
--- a/common/main/fuelcen.h
+++ b/common/main/fuelcen.h
@@ -87,8 +87,6 @@ fix repaircen_give_shields(segment *segp, fix MaxAmountCanTake );
 #define MAX_NUM_FUELCENS    70
 #endif
 
-extern const char Special_names[MAX_CENTER_TYPES][11];
-
 //--repair-- //do the repair center for this frame
 //--repair-- void do_repair_sequence(object *obj);
 //--repair--
@@ -128,6 +126,7 @@ typedef struct  {
 	short   fuelcen_num;    // Index in fuelcen array.
 } __pack__ d1_matcen_info;
 
+#if defined(DXX_BUILD_DESCENT_I) || defined(DXX_BUILD_DESCENT_II)
 #if defined(DXX_BUILD_DESCENT_I)
 typedef d1_matcen_info matcen_info;
 #elif defined(DXX_BUILD_DESCENT_II)
@@ -140,7 +139,11 @@ typedef struct matcen_info {
 } __pack__ matcen_info;
 #endif
 
+extern const char Special_names[MAX_CENTER_TYPES][11];
+
 extern matcen_info RobotCenters[MAX_ROBOT_CENTERS];
+extern FuelCenter Station[MAX_NUM_FUELCENS];
+#endif
 
 //--repair-- extern object *RepairObj;  // which object getting repaired, or NULL
 
@@ -150,13 +153,13 @@ extern void trigger_matcen(int segnum);
 
 extern void disable_matcens(void);
 
-extern FuelCenter Station[MAX_NUM_FUELCENS];
 extern int Num_fuelcenters;
 
 extern void init_all_matcens(void);
 
 extern const fix EnergyToCreateOneRobot;
 
+#if defined(DXX_BUILD_DESCENT_I) || defined(DXX_BUILD_DESCENT_II)
 #if defined(DXX_BUILD_DESCENT_I)
 /*
  * reads a matcen_info structure from a PHYSFS_file
@@ -182,6 +185,7 @@ void matcen_info_read(matcen_info *ps, PHYSFS_file *fp);
 void matcen_info_read_n_swap(matcen_info *mi, int n, int swap, PHYSFS_file *fp);
 
 void matcen_info_write(matcen_info *mi, short version, PHYSFS_file *fp);
+#endif
 
 /*
  * reads n Station structs from a PHYSFS_file and swaps if specified
diff --git a/common/main/gameseq.h b/common/main/gameseq.h
index 4e84717e0..71b2e1aa5 100644
--- a/common/main/gameseq.h
+++ b/common/main/gameseq.h
@@ -27,6 +27,8 @@ COPYRIGHT 1993-1999 PARALLAX SOFTWARE CORPORATION.  ALL RIGHTS RESERVED.
 
 #ifdef __cplusplus
 
+struct player;
+
 #define SUPER_MISSILE       0
 #define SUPER_SEEKER        1
 #define SUPER_SMARTBOMB     2
diff --git a/common/main/multi.h b/common/main/multi.h
index 9daf30c5b..7d8a64a2e 100644
--- a/common/main/multi.h
+++ b/common/main/multi.h
@@ -251,7 +251,6 @@ enum multiplayer_command_t {
 	VALUE(NETFLAG_DOHEADLIGHT, "Headlight")	\
 
 #endif
-#endif
 
 #define define_netflag_bit_enum(NAME,STR)	BIT_##NAME,
 #define define_netflag_bit_mask(NAME,STR)	NAME = (1 << BIT_##NAME),
@@ -261,6 +260,18 @@ enum { for_each_netflag_value(define_netflag_bit_enum) };
 enum { for_each_netflag_value(define_netflag_bit_mask) };
 enum { NETFLAG_DOPOWERUP = 0 for_each_netflag_value(define_netflag_powerup_mask) };
 
+extern const char multi_allow_powerup_text[MULTI_ALLOW_POWERUP_MAX][MULTI_ALLOW_POWERUP_TEXT_LENGTH];
+extern const char GMNames[MULTI_GAME_TYPE_COUNT][MULTI_GAME_NAME_LENGTH];
+extern const char GMNamesShrt[MULTI_GAME_TYPE_COUNT][8];
+
+extern ubyte multibuf[MAX_MULTI_MESSAGE_LEN+4];
+extern int Net_create_objnums[MAX_NET_CREATE_OBJECTS];
+extern int Net_create_loc;
+
+extern char PowerupsInMine[MAX_POWERUP_TYPES],
+	MaxPowerupsAllowed[MAX_POWERUP_TYPES];
+#endif
+
 enum msgsend_state_t {
 	msgsend_none,
 	msgsend_typing,
@@ -272,10 +283,6 @@ enum deres_type_t {
 	deres_drop,
 };
 
-extern const char multi_allow_powerup_text[MULTI_ALLOW_POWERUP_MAX][MULTI_ALLOW_POWERUP_TEXT_LENGTH];
-extern const char GMNames[MULTI_GAME_TYPE_COUNT][MULTI_GAME_NAME_LENGTH];
-extern const char GMNamesShrt[MULTI_GAME_TYPE_COUNT][8];
-
 // Exported functions
 
 extern int GetMyNetRanking();
@@ -379,13 +386,8 @@ extern int VerifyPlayerJoined;
 extern int Player_joining_extras;
 extern int Network_player_added;
 
-extern ubyte multibuf[MAX_MULTI_MESSAGE_LEN+4];
-
 extern int who_killed_controlcen;
 
-extern int Net_create_objnums[MAX_NET_CREATE_OBJECTS];
-extern int Net_create_loc;
-
 extern short kill_matrix[MAX_PLAYERS][MAX_PLAYERS];
 extern short team_kills[2];
 
@@ -421,8 +423,6 @@ extern int Bounty_target;
 extern bitmap_index multi_player_textures[MAX_PLAYERS][N_PLAYER_SHIP_TEXTURES];
 
 extern const char RankStrings[10][14];
-extern char PowerupsInMine[MAX_POWERUP_TYPES],
-	MaxPowerupsAllowed[MAX_POWERUP_TYPES];
 
 // Globals for protocol-bound Refuse-functions
 extern char RefuseThisPlayer,WaitForRefuseAnswer,RefuseTeam,RefusePlayerName[12];
diff --git a/common/main/multibot.h b/common/main/multibot.h
index f5fd5811e..a6d3f80cf 100644
--- a/common/main/multibot.h
+++ b/common/main/multibot.h
@@ -28,6 +28,7 @@ COPYRIGHT 1993-1999 PARALLAX SOFTWARE CORPORATION.  ALL RIGHTS RESERVED.
 struct object;
 struct vms_vector;
 
+#if defined(DXX_BUILD_DESCENT_I) || defined(DXX_BUILD_DESCENT_II)
 #if defined(DXX_BUILD_DESCENT_I)
 #define MAX_ROBOTS_CONTROLLED 3
 #elif defined(DXX_BUILD_DESCENT_II)
@@ -37,6 +38,7 @@ struct vms_vector;
 extern int robot_controlled[MAX_ROBOTS_CONTROLLED];
 extern int robot_agitation[MAX_ROBOTS_CONTROLLED];
 extern int robot_fired[MAX_ROBOTS_CONTROLLED];
+#endif
 
 int multi_can_move_robot(int objnum, int agitation);
 void multi_send_robot_position(int objnum, int fired);
diff --git a/common/main/powerup.h b/common/main/powerup.h
index 09789efd8..db7564052 100644
--- a/common/main/powerup.h
+++ b/common/main/powerup.h
@@ -95,6 +95,7 @@ enum powerup_type_t
 #endif
 };
 
+#if defined(DXX_BUILD_DESCENT_I) || defined(DXX_BUILD_DESCENT_II)
 #if defined(DXX_BUILD_DESCENT_I)
 #define VULCAN_AMMO_MAX             (392*2)
 #define MAX_POWERUP_TYPES			29
@@ -119,6 +120,9 @@ typedef struct powerup_type_info {
 
 extern int N_powerup_types;
 extern powerup_type_info Powerup_info[MAX_POWERUP_TYPES];
+#else
+struct powerup_type_info;
+#endif
 
 void draw_powerup(object *obj);
 
diff --git a/common/main/robot.h b/common/main/robot.h
index a16afca05..8bd401269 100644
--- a/common/main/robot.h
+++ b/common/main/robot.h
@@ -175,10 +175,10 @@ static inline int robot_is_thief(const robot_info *robptr)
 #define ROBOT_NAME_LENGTH   16
 #if defined(DXX_BUILD_DESCENT_I) || defined(DXX_BUILD_DESCENT_II)
 extern char Robot_names[MAX_ROBOT_TYPES][ROBOT_NAME_LENGTH];
-#endif
 
 //the array of robots types
 extern robot_info Robot_info[MAX_ROBOT_TYPES];     // Robot info for AI system, loaded from bitmaps.tbl.
+#endif
 
 //how many kinds of robots
 extern  int N_robot_types;      // Number of robot types.  We used to assume this was the same as N_polygon_models.
diff --git a/common/main/switch.h b/common/main/switch.h
index ac5ed6464..f80671e2d 100644
--- a/common/main/switch.h
+++ b/common/main/switch.h
@@ -119,7 +119,6 @@ typedef struct trigger {
 	short   seg[MAX_WALLS_PER_LINK];
 	short   side[MAX_WALLS_PER_LINK];
 } __pack__ trigger;
-#endif
 
 extern trigger Triggers[MAX_TRIGGERS];
 
@@ -175,3 +174,5 @@ extern void trigger_write(trigger *t, short version, PHYSFS_file *fp);
 #endif
 
 #endif
+
+#endif
diff --git a/common/main/text.h b/common/main/text.h
index b2285005b..7987de790 100644
--- a/common/main/text.h
+++ b/common/main/text.h
@@ -1275,6 +1275,7 @@ void decode_text(char *text, int len);  // decryption for briefings, etc.
 void load_text(void);
 void free_text();
 
+#if defined(DXX_BUILD_DESCENT_I) || defined(DXX_BUILD_DESCENT_II)
 #ifndef USE_BUILTIN_ENGLISH_TEXT_STRINGS
 //Array of pointers to text
 extern const char *Text_string[N_TEXT_STRINGS];
@@ -1291,6 +1292,7 @@ static inline const char *dxx_gettext(unsigned expr, const char *fmt)
 	return Text_string[expr];
 #endif
 }
+#endif
 
 #endif
 
diff --git a/common/main/textures.h b/common/main/textures.h
index e404a4792..5fcdd48e0 100644
--- a/common/main/textures.h
+++ b/common/main/textures.h
@@ -21,6 +21,7 @@ COPYRIGHT 1993-1999 PARALLAX SOFTWARE CORPORATION.  ALL RIGHTS RESERVED.
 #ifndef _TEXTURES_H
 #define _TEXTURES_H
 
+#if defined(DXX_BUILD_DESCENT_I) || defined(DXX_BUILD_DESCENT_II)
 #include "bm.h"
 #include "piggy.h"
 
@@ -28,5 +29,6 @@ COPYRIGHT 1993-1999 PARALLAX SOFTWARE CORPORATION.  ALL RIGHTS RESERVED.
 
 extern int NumTextures;
 extern bitmap_index Textures[MAX_TEXTURES]; // Array of all texture tmaps.
+#endif
 
 #endif /* _TEXTURES_H */
diff --git a/common/main/wall.h b/common/main/wall.h
index f27147f3a..84570704b 100644
--- a/common/main/wall.h
+++ b/common/main/wall.h
@@ -191,6 +191,7 @@ typedef struct cloaking_wall {
 #define WCF_TMAP1       4       //this uses primary tmap, not tmap2
 #define WCF_HIDDEN      8       //this uses primary tmap, not tmap2
 
+#if defined(DXX_BUILD_DESCENT_I) || defined(DXX_BUILD_DESCENT_II)
 typedef struct {
 	fix     play_time;
 	short   num_frames;
@@ -222,6 +223,10 @@ extern wclip WallAnims[MAX_WALL_ANIMS];
 extern int Num_wall_anims;
 
 extern int walls_bm_num[MAX_WALL_ANIMS];
+#else
+struct wall;
+struct wclip;
+#endif
 
 // Initializes all walls (i.e. no special walls.)
 extern void wall_init();