diff --git a/build b/build
index edfa6fc..477c328 100644
--- a/build
+++ b/build
@@ -1,11 +1,12 @@
 rm lerc1dec.* *.o
-emcc -O3 -c lerc1Image.cpp
-emcc -O3 -c lerc1api.cpp
-emcc -O3 -c rasterfunk.cpp
+OPTS="-O3 -flto"
+emcc $OPTS -c lerc1Image.cpp
+emcc $OPTS -c lerc1api.cpp
+emcc $OPTS -ffast-math -c rasterfunk.cpp
 
 # Build the test app
-# emcc -O3 -o lercapp.html app.cpp lerc1api.o lerc1Image.o --preload-file 0 -sUSE_SDL=2
+# emcc $OPTS -o lercapp.html app.cpp lerc1api.o lerc1Image.o --preload-file 0 -sUSE_SDL=2
 
 # Build a lerc1.wasm library, with just the lerc1api exported
 EXPORTS=_malloc,_free
-emcc -O3 -o lerc1dec.js lerc1api.o lerc1Image.o rasterfunk.o -sNO_EXIT_RUNTIME=1 -sEXPORTED_FUNCTIONS=$EXPORTS --no-entry -sEXPORTED_RUNTIME_METHODS=[cwrap,writeArrayToMemory,UTF8ToString]
+emcc $OPTS -o lerc1dec.js lerc1api.o lerc1Image.o rasterfunk.o -sNO_EXIT_RUNTIME=1 -sEXPORTED_FUNCTIONS=$EXPORTS --no-entry -sEXPORTED_RUNTIME_METHODS=[cwrap,writeArrayToMemory,UTF8ToString]
diff --git a/docs/lerc1dec.wasm b/docs/lerc1dec.wasm
index d7e1ba9..879be9a 100644
Binary files a/docs/lerc1dec.wasm and b/docs/lerc1dec.wasm differ
diff --git a/rasterfunk.cpp b/rasterfunk.cpp
index 7592833..c07da1c 100644
--- a/rasterfunk.cpp
+++ b/rasterfunk.cpp
@@ -55,7 +55,7 @@ int hillshade(float *data, size_t sz, double pixel_size, double sun_angle, uint3
 
     constexpr int TILESIZE(256);
     constexpr int DATATILESIZE(257);
-    constexpr uint32_t ALPHA(0xff000000);
+    constexpr uint32_t OPAQUE(0xff000000);
     constexpr auto base(32.0); // baseline brightness
     constexpr auto rescale((256 - base) / 256); // brightness rescale factor
     for (int y = 0; y < TILESIZE; y++)
@@ -75,12 +75,13 @@ int hillshade(float *data, size_t sz, double pixel_size, double sun_angle, uint3
             uint32_t red = val & 0xff;
             uint32_t green = (val >> 8) & 0xff;
             uint32_t blue = (val >> 16) & 0xff;
-            uint32_t alpha = (val >> 24) & 0xff;
             red = (base + rescale * red) * factor;
             green = (base + rescale * green) * factor;
             blue = (base + rescale * blue) * factor;
+            // alpha is unaffected by hillshade
+            uint32_t alpha = val & OPAQUE;
 
-            pixels[TILESIZE * y + x] = ALPHA | (blue << 16) | (green << 8) | red;
+            pixels[TILESIZE * y + x] = alpha | (blue << 16) | (green << 8) | red;
         }
     }
     return 1;