diff --git a/src/net.ts b/src/net.ts
index d743375..44d0fa8 100644
--- a/src/net.ts
+++ b/src/net.ts
@@ -49,8 +49,8 @@ export const signedFetch = async (url: string, init: RequestInit, signedInit: Si
     signedHeaders.push(["Signature", signature]);
 
     const newHeaders = new Headers();
-    if (Array.isArray(init.headers)) {
-        for (const header of init.headers) {
+    if (Array.isArray(init.headers) || !init.headers) {
+        for (const header of (init.headers || [])) {
             if (Array.isArray(header))
                 newHeaders.set(header[0], header[1]);
             else throw "unsupported headers type"; // Lazy.