diff --git a/packages/opencode/src/provider/provider.ts b/packages/opencode/src/provider/provider.ts
index cdbad663784..30ca52f1016 100644
--- a/packages/opencode/src/provider/provider.ts
+++ b/packages/opencode/src/provider/provider.ts
@@ -5,6 +5,7 @@ import { Config } from "../config/config"
 import { mapValues, mergeDeep, omit, pickBy, sortBy } from "remeda"
 import { NoSuchModelError, type Provider as SDK } from "ai"
 import { Log } from "../util/log"
+import { sanitizeSurrogates } from "../util/sanitize-surrogates"
 import { BunProc } from "../bun"
 import { Plugin } from "../plugin"
 import { ModelsDev } from "./models"
@@ -1093,6 +1094,10 @@ export namespace Provider {
           }
         }
 
+        if (typeof opts.body === "string") {
+          opts.body = sanitizeSurrogates(opts.body)
+        }
+
         return fetchFn(input, {
           ...opts,
           // @ts-ignore see here: https://github.com/oven-sh/bun/issues/16682
diff --git a/packages/opencode/src/util/sanitize-surrogates.test.ts b/packages/opencode/src/util/sanitize-surrogates.test.ts
new file mode 100644
index 00000000000..d18b8fb8f54
--- /dev/null
+++ b/packages/opencode/src/util/sanitize-surrogates.test.ts
@@ -0,0 +1,38 @@
+import { describe, test, expect } from "bun:test"
+import { sanitizeSurrogates } from "./sanitize-surrogates"
+
+describe("sanitizeSurrogates", () => {
+  test("replaces lone high surrogate", () => {
+    expect(sanitizeSurrogates("\uD800")).toBe("\uFFFD")
+  })
+
+  test("replaces lone low surrogate", () => {
+    expect(sanitizeSurrogates("\uDC00")).toBe("\uFFFD")
+  })
+
+  test("preserves valid surrogate pair", () => {
+    const emoji = "\uD83D\uDE00"
+    expect(sanitizeSurrogates(emoji)).toBe(emoji)
+  })
+
+  test("preserves normal text", () => {
+    expect(sanitizeSurrogates("hello world")).toBe("hello world")
+  })
+
+  test("preserves Korean text", () => {
+    expect(sanitizeSurrogates("안녕하세요")).toBe("안녕하세요")
+  })
+
+  test("preserves empty string", () => {
+    expect(sanitizeSurrogates("")).toBe("")
+  })
+
+  test("replaces surrogate in middle", () => {
+    expect(sanitizeSurrogates("hello\uD800world")).toBe("hello\uFFFDworld")
+  })
+
+  test("result is well-formed", () => {
+    const result = sanitizeSurrogates("test\uD800\uDBFF\uDC00data\uDFFF")
+    expect(result.isWellFormed()).toBe(true)
+  })
+})
diff --git a/packages/opencode/src/util/sanitize-surrogates.ts b/packages/opencode/src/util/sanitize-surrogates.ts
new file mode 100644
index 00000000000..1de3fdbbcd3
--- /dev/null
+++ b/packages/opencode/src/util/sanitize-surrogates.ts
@@ -0,0 +1,6 @@
+export function sanitizeSurrogates(s: string): string {
+  if (typeof s !== "string" || s.length === 0) return s
+  if (typeof s.isWellFormed === "function" && s.isWellFormed()) return s
+  if (typeof s.toWellFormed === "function") return s.toWellFormed()
+  return s.replace(/[\uD800-\uDBFF](?![\uDC00-\uDFFF])|(?<![\uD800-\uDBFF])[\uDC00-\uDFFF]/g, "\uFFFD")
+}