diff --git a/source/games/duke/src/premap_d.cpp b/source/games/duke/src/premap_d.cpp
index 9cf927c1e..0373407c0 100644
--- a/source/games/duke/src/premap_d.cpp
+++ b/source/games/duke/src/premap_d.cpp
@@ -40,6 +40,7 @@ BEGIN_DUKE_NS
 
 inline void tloadtile(int tilenum, int palnum = 0)
 {
+    assert(tilenum < MAXTILES);
 	markTileForPrecache(tilenum, palnum);
 }
 
diff --git a/source/glbackend/glbackend.cpp b/source/glbackend/glbackend.cpp
index f8a0534b1..9b5ad1254 100644
--- a/source/glbackend/glbackend.cpp
+++ b/source/glbackend/glbackend.cpp
@@ -482,7 +482,7 @@ void markTileForPrecache(int tilenum, int palnum)
 
 	for (; i <= j; i++)
 	{
-		int64_t val = i + (int64_t(palnum) << 16);
+		int64_t val = i + (int64_t(palnum) << 32);
 		cachemap.Insert(val, true);
 	}
 }
@@ -495,7 +495,7 @@ void precacheMarkedTiles()
 	decltype(cachemap)::Pair* pair;
 	while (it.NextPair(pair))
 	{
-		int dapicnum = pair->Key;
+		int dapicnum = pair->Key & 0x7fffffff;
 		int dapalnum = pair->Key >> 32;
 		polymost_precache(dapicnum, dapalnum, 0);
 	}