diff --git a/Descent3/terrain.h b/Descent3/terrain.h
index 53c87f65a..1037732ef 100644
--- a/Descent3/terrain.h
+++ b/Descent3/terrain.h
@@ -213,7 +213,18 @@ extern terrain_tex_segment Terrain_tex_seg[TERRAIN_TEX_WIDTH * TERRAIN_TEX_DEPTH
 // first object to render after cell has been rendered (only used for SW renderer)
 extern short Terrain_seg_render_objs[];
 
+#ifdef RELEASE
 #define TERRAIN_REGION(x) ((Terrain_seg[0x7FFFFFFF & x].flags & TFM_REGION_MASK) >> 5)
+#else // debug(-ish) builds - check if x is valid
+inline int TERRAIN_REGION(int x) {
+	ASSERT(x != -1 && "invalid/unset room number (-1)!");
+	// Note: due to the 0x7FFFFFFF mask, terrSegIdx will be >= 0
+	int terrSegIdx = 0x7FFFFFFF & x;
+	// catch other invalid cell/segment numbers than -1 as well
+	ASSERT((terrSegIdx < TERRAIN_WIDTH * TERRAIN_DEPTH) && "invalid cellnum!");
+	return (Terrain_seg[terrSegIdx].flags & TFM_REGION_MASK) >> 5;
+}
+#endif
 
 extern terrain_sky Terrain_sky;
 
diff --git a/sndlib/hlsoundlib.cpp b/sndlib/hlsoundlib.cpp
index cdbd9b4a5..2075d87e0 100644
--- a/sndlib/hlsoundlib.cpp
+++ b/sndlib/hlsoundlib.cpp
@@ -922,6 +922,17 @@ bool hlsSystem::ComputePlayInfo(int sound_obj_index, vector *virtual_pos, vector
     sound_seg = m_sound_objects[sound_obj_index].m_link_info.pos_info.segnum;
   }
 
+  // sound_seg == -1 (which just means that the roomnum/segnum hasn't been
+  // initialized to a proper value yet )causes crashes when BOA_INDEX()
+  // calls TERRAIN_REGION() with that value. (By pure luck on 32bit platforms
+  // the overflow and truncation will likely use an address that doesn't crash,
+  // but it's still invalid). At least one case that could cause this was fixed,
+  // if there are others, the ASSERT should tell us about it
+  // (and if assertions are disabled, return false to handle this gracefully)
+  ASSERT(sound_seg != -1 && "invalid (unset) roomnum/segnum!");
+  if (sound_seg == -1)
+    return false;
+
   sound_seg = BOA_INDEX(sound_seg);
   ear_seg = BOA_INDEX(Viewer_object->roomnum);
   if (!BOA_IsSoundAudible(sound_seg, ear_seg))
@@ -1079,6 +1090,13 @@ int hlsSystem::Play3dSound(int sound_index, pos_state *cur_pos, object *cur_obj,
     return -1;
   if (sound_index >= MAX_SOUNDS || Sounds[sound_index].used == 0)
     return -1;
+  // if the position doesn't belong to any valid room or cell,
+  // all this would fail anyway (in Emulate3dSound() -> ComputePlayInfo()),
+  // so might as well give up now; furthermore, this prevents m_sound_objects[i]
+  // from remaining in an half-initialized state below (esp. for looping sounds
+  // where StopSound() wouldn't be called after Emulate3dSound() returns false)
+  if (cur_pos->roomnum == -1)
+    return -1;
   // initialize sound.
   Sound_system.CheckAndForceSoundDataAlloc(sound_index);
   int sample_offset = offset * 22050.0f;