diff --git a/alg/Makefile b/alg/Makefile
index 9479175..5f67778 100644
--- a/alg/Makefile
+++ b/alg/Makefile
@@ -74,7 +74,7 @@ SIMD128_OPTS :=
 
 qrtool.wx.js: pre.wx.js post.wx.js
 qrtool.wx.js qrtool.web.js: qrtool_wasm.cpp libqr.cpp Makefile
-	emcc \
+	source ../../emsdk/emsdk_env.sh && emcc \
 		-o $@ -I$(CV_INSTALL_DIR)/include/opencv4 $(filter %.cpp, $^) \
 		$(addprefix $(CV_WASM_DIR)/lib/, \
 		libopencv_core.a \