diff --git a/packages/npm-packages/ruby-wasm-wasi/src/browser.ts b/packages/npm-packages/ruby-wasm-wasi/src/browser.ts
index f724df1ac1..c0523698d8 100644
--- a/packages/npm-packages/ruby-wasm-wasi/src/browser.ts
+++ b/packages/npm-packages/ruby-wasm-wasi/src/browser.ts
@@ -46,6 +46,9 @@ export const DefaultRubyVM = async (
   await vm.setInstance(instance);
 
   wasi.setMemory(instance.exports.memory as WebAssembly.Memory);
+  // Manually call `_initialize`, which is a part of reactor modoel ABI,
+  // because the WASI polyfill doesn't support it yet.
+  (instance.exports._initialize as Function)();
   vm.initialize();
 
   return {