diff --git a/overviewer_core/src/overviewer.h b/overviewer_core/src/overviewer.h
index e20c15f..75d2894 100644
--- a/overviewer_core/src/overviewer.h
+++ b/overviewer_core/src/overviewer.h
@@ -147,6 +147,7 @@ block_has_property(unsigned short b, BlockProperty prop) {
     return block_properties[b] & (1 << prop);
 }
 #define is_transparent(b) block_has_property((b), TRANSPARENT)
+#define is_known_transparent(b) block_has_property((b), TRANSPARENT) && block_has_property((b), KNOWN)
 
 /* helper for indexing section data possibly across section boundaries */
 typedef enum
diff --git a/overviewer_core/src/primitives/cave.c b/overviewer_core/src/primitives/cave.c
index 064f498..c89ccfc 100644
--- a/overviewer_core/src/primitives/cave.c
+++ b/overviewer_core/src/primitives/cave.c
@@ -43,9 +43,9 @@ cave_occluded(void *data, RenderState *state, int x, int y, int z) {
     /* check for normal occlusion */
     /* use ajacent chunks, if not you get blocks spreaded in chunk edges */
 
-    if (!is_transparent(get_data(state, BLOCKS, x-1, y, z)) &&
-        !is_transparent(get_data(state, BLOCKS, x, y, z+1)) &&
-        !is_transparent(get_data(state, BLOCKS, x, y+1, z))) {
+    if (!is_known_transparent(get_data(state, BLOCKS, x-1, y, z)) &&
+        !is_known_transparent(get_data(state, BLOCKS, x, y, z+1)) &&
+        !is_known_transparent(get_data(state, BLOCKS, x, y+1, z))) {
         return 1;
     }