diff --git a/src/interpreter_extra.cc b/src/interpreter_extra.cc
index fa9365e..221f4a5 100644
--- a/src/interpreter_extra.cc
+++ b/src/interpreter_extra.cc
@@ -2210,7 +2210,7 @@ static void opSetExitGrids(Program* program)
 
     Object* object = objectFindFirstAtElevation(elevation);
     while (object != NULL) {
-        if (object->pid >= PROTO_ID_0x5000010 && object->pid <= PROTO_ID_0x5000017) {
+        if (object->pid >= FIRST_EXIT_GRID_PID && object->pid <= LAST_EXIT_GRID_PID) {
             object->data.misc.map = destinationMap;
             object->data.misc.tile = destinationTile;
             object->data.misc.elevation = destinationElevation;
diff --git a/src/object.cc b/src/object.cc
index eb078ee..3bf12ea 100644
--- a/src/object.cc
+++ b/src/object.cc
@@ -438,16 +438,16 @@ int objectRead(Object* obj, File* stream)
         return -1;
     }
 
-    if (obj->pid < 0x5000010 || obj->pid > 0x5000017) {
-        if (PID_TYPE(obj->pid) == 0 && !(gMapHeader.flags & 0x01)) {
-            _object_fix_weapon_ammo(obj);
-        }
-    } else {
+    if (isExitGridPid(obj->pid)) {
         if (obj->data.misc.map <= 0) {
             if ((obj->fid & 0xFFF) < 33) {
                 obj->fid = buildFid(OBJ_TYPE_MISC, (obj->fid & 0xFFF) + 16, FID_ANIM_TYPE(obj->fid), 0, 0);
             }
         }
+    } else {
+        if (PID_TYPE(obj->pid) == 0 && !(gMapHeader.flags & 0x01)) {
+            _object_fix_weapon_ammo(obj);
+        }
     }
 
     return 0;
@@ -1469,7 +1469,7 @@ int objectSetLocation(Object* obj, int tile, int elevation, Rect* rect)
 
             if (elevation == elev) {
                 if (FID_TYPE(obj->fid) == OBJ_TYPE_MISC) {
-                    if (obj->pid >= 0x5000010 && obj->pid <= 0x5000017) {
+                    if (isExitGridPid(obj->pid)) {
                         ObjectData* data = &(obj->data);
 
                         MapTransition transition;
diff --git a/src/proto.cc b/src/proto.cc
index 7e979cc..86d767b 100644
--- a/src/proto.cc
+++ b/src/proto.cc
@@ -519,7 +519,7 @@ int objectDataRead(Object* obj, File* stream)
 
             break;
         case OBJ_TYPE_MISC:
-            if (obj->pid >= 0x5000010 && obj->pid <= 0x5000017) {
+            if (isExitGridPid(obj->pid)) {
                 if (fileReadInt32(stream, &(obj->data.misc.map)) == -1) return -1;
                 if (fileReadInt32(stream, &(obj->data.misc.tile)) == -1) return -1;
                 if (fileReadInt32(stream, &(obj->data.misc.elevation)) == -1) return -1;
@@ -600,7 +600,7 @@ int objectDataWrite(Object* obj, File* stream)
             }
             break;
         case OBJ_TYPE_MISC:
-            if (obj->pid >= 0x5000010 && obj->pid <= 0x5000017) {
+            if (isExitGridPid(obj->pid)) {
                 if (fileWriteInt32(stream, data->misc.map) == -1) return -1;
                 if (fileWriteInt32(stream, data->misc.tile) == -1) return -1;
                 if (fileWriteInt32(stream, data->misc.elevation) == -1) return -1;
@@ -674,7 +674,7 @@ static int _proto_update_gen(Object* obj)
         }
         break;
     case OBJ_TYPE_MISC:
-        if (obj->pid >= 0x5000010 && obj->pid <= 0x5000017) {
+        if (isExitGridPid(obj->pid)) {
             data->misc.tile = -1;
             data->misc.elevation = 0;
             data->misc.rotation = 0;
diff --git a/src/proto.h b/src/proto.h
index 1b27ce0..c7f481d 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -126,6 +126,11 @@ void _proto_remove_all();
 int protoGetProto(int pid, Proto** out_proto);
 int _ResetPlayer();
 
+static bool isExitGridPid(int pid)
+{
+    return pid >= FIRST_EXIT_GRID_PID && pid <= LAST_EXIT_GRID_PID;
+}
+
 } // namespace fallout
 
 #endif /* PROTO_H */
diff --git a/src/proto_types.h b/src/proto_types.h
index 1095b5a..df7aac2 100644
--- a/src/proto_types.h
+++ b/src/proto_types.h
@@ -198,10 +198,8 @@ enum {
 #define PROTO_ID_0x20001D6 0x20001D6
 #define PROTO_ID_0x20001EB 0x20001EB
 #define FID_0x20001F5 0x20001F5
-// first exit grid
-#define PROTO_ID_0x5000010 0x5000010
-// last exit grid
-#define PROTO_ID_0x5000017 0x5000017
+#define FIRST_EXIT_GRID_PID 0x5000010
+#define LAST_EXIT_GRID_PID 0x5000017
 
 typedef enum ItemProtoFlags {
     ItemProtoFlags_0x08 = 0x08,