diff --git a/src/utils.ts b/src/utils.ts
index a773431b..ff7871a0 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -18,8 +18,11 @@ export function isJSONSerializable(value: any): boolean {
   if (value === undefined) {
     return false;
   }
+  if (value === null) {
+    return true;
+  }
   const t = typeof value;
-  if (t === "string" || t === "number" || t === "boolean" || t === null) {
+  if (t === "string" || t === "number" || t === "boolean") {
     return true;
   }
   if (t !== "object") {
@@ -28,14 +31,14 @@ export function isJSONSerializable(value: any): boolean {
   if (Array.isArray(value)) {
     return true;
   }
-  if (value.buffer) {
-    return false;
-  }
   // `FormData` and `URLSearchParams` should't have a `toJSON` method,
   // but Bun adds it, which is non-standard.
   if (value instanceof FormData || value instanceof URLSearchParams) {
     return false;
   }
+  if (value.buffer) {
+    return false;
+  }
   return (
     (value.constructor && value.constructor.name === "Object") ||
     typeof value.toJSON === "function"
diff --git a/test/index.test.ts b/test/index.test.ts
index 5ac20b07..c3f7a848 100644
--- a/test/index.test.ts
+++ b/test/index.test.ts
@@ -525,3 +525,25 @@ describe("ofetch", () => {
     });
   });
 });
+
+describe("isJSONSerializable", () => {
+  let isJSONSerializable: (value: unknown) => boolean;
+
+  beforeAll(async () => {
+    const utils = await import("../src/utils.ts");
+    isJSONSerializable = utils.isJSONSerializable;
+  });
+
+  it("returns false for FormData and URLSearchParams before buffer checks", () => {
+    expect(isJSONSerializable(new FormData())).toBe(false);
+    expect(isJSONSerializable(new URLSearchParams())).toBe(false);
+
+    const data = new FormData();
+    data.append("foo", "bar");
+    expect(isJSONSerializable(data)).toBe(false);
+  });
+
+  it("returns true for null without throwing", () => {
+    expect(isJSONSerializable(null)).toBe(true); // eslint-disable-line unicorn/no-null
+  });
+});