diff --git a/app/build.sh b/app/build.sh
index ab5f515..7a9fc28 100755
--- a/app/build.sh
+++ b/app/build.sh
@@ -1,5 +1,27 @@
 #! /bin/sh
 
 cd $(dirname $0)
+if ! which wasm-pack > /dev/null 2>&1
+then
+  >&2 echo '`wasm-pack` not found. Try running `cargo install wasm-pack`'
+  exit 1
+fi
+
 wasm-pack build --target web
-rollup ./main.js --format iife --file ./pkg/bundle.js
+
+ROLLUP_BIN=$(which rollup 2>/dev/null)
+if [ -f ../node_modules/rollup/dist/bin/rollup ]
+then
+  ROLLUP_BIN=../node_modules/rollup/dist/bin/rollup
+elif [ -f node_modules/rollup/dist/bin/rollup ]
+then
+  ROLLUP_BIN=node_modules/rollup/dist/bin/rollup
+fi
+
+if [ -z "$ROLLUP_BIN" ]
+then
+  >&2 echo '`rollup` not found. Try running `npm install rollup`'
+  exit 1
+fi
+
+$ROLLUP_BIN ./main.js --format iife --file ./pkg/bundle.js