diff --git a/Makefile.simple b/Makefile.simple
index 7394943c..7c626a61 100644
--- a/Makefile.simple
+++ b/Makefile.simple
@@ -160,7 +160,7 @@ savepng$(OBJ_EXTENSION): savepng.cpp
 emscripten: hyper.html
 
 %.html %.js %.wasm: %.emscripten-sources
-	emcc -std=c++11 -O3 -s LEGACY_GL_EMULATION=1 -s TOTAL_MEMORY=128MB hyperweb.cpp -o hyper.html
+	emcc -std=c++11 -O3 -s USE_ZLIB=1 -s LEGACY_GL_EMULATION=1 -s TOTAL_MEMORY=128MB hyperweb.cpp -o hyper.html
 
 hyper.emscripten-sources: *.cpp autohdr.h