diff --git a/um_wasm_loader/build.js b/um_wasm_loader/build.js
index df4efda..605c6d1 100644
--- a/um_wasm_loader/build.js
+++ b/um_wasm_loader/build.js
@@ -56,13 +56,30 @@ async function replaceFileByRegex(filepath, ...replacementRules) {
   await writeFile(filepath, content, 'utf-8');
 }
 
+/**
+ * @param {string | undefined} value
+ * @param [defaultValue=false]
+ * @return {boolean}
+ */
+function parseBoolean(value, defaultValue = false) {
+  if (value === undefined || value === null) {
+    return defaultValue;
+  }
+
+  if (Number.isFinite(+value)) {
+    return Boolean(value);
+  }
+
+  return value.toLowerCase() === 'true';
+}
+
 async function main() {
   const wasmSourceDir = path.join(__dirname, '..', 'um_wasm');
   const wasmOutDir = path.resolve(__dirname, 'pkg');
   const wasmDistDir = path.resolve(__dirname, 'dist');
   await rm(wasmOutDir, { recursive: true, force: true });
   const wasmRelOutDir = path.relative(wasmSourceDir, wasmOutDir);
-  const profileFlag = process.env.BUILD_RELEASE ? '--release' : '--dev';
+  const profileFlag = parseBoolean(process.env.BUILD_RELEASE, true) ? '--release' : '--dev';
   await run(['wasm-pack', 'build', profileFlag, '--target', 'web', '--out-dir', wasmRelOutDir], {
     cwd: path.resolve(__dirname, '..', 'um_wasm'),
   });