diff --git a/src/commit.ts b/src/commit.ts
index 296086c..a11bdd5 100644
--- a/src/commit.ts
+++ b/src/commit.ts
@@ -84,12 +84,26 @@ export function parseRawCommit(oid: string, raw: string): Commit {
     );
   }
 
-  if (headers.some((line) => line.startsWith("gpgsig "))) {
+  if (
+    headers.some(
+      (line) => line.startsWith("gpgsig ") || line.startsWith("gpgsig-sha256 "),
+    )
+  ) {
     throw new Error(
       `Commit ${oid} is signed. bstack cannot add an identity trailer without replacing its signature`,
     );
   }
 
+  const encoding = headers
+    .find((line) => line.startsWith("encoding "))
+    ?.slice("encoding ".length);
+
+  if (encoding && !/^utf-?8$/i.test(encoding)) {
+    throw new Error(
+      `Commit ${oid} uses the ${encoding} message encoding; bstack only supports UTF-8 commit messages`,
+    );
+  }
+
   const message = raw.slice(boundary + 2);
 
   return {
diff --git a/test/commit.test.ts b/test/commit.test.ts
index f138c44..f2e85ba 100644
--- a/test/commit.test.ts
+++ b/test/commit.test.ts
@@ -53,6 +53,42 @@ describe("commit identity", () => {
     });
   });
 
+  test.each([
+    ["gpgsig -----BEGIN PGP SIGNATURE-----", "is signed"],
+    ["gpgsig-sha256 -----BEGIN PGP SIGNATURE-----", "is signed"],
+    ["encoding ISO-8859-1", "uses the ISO-8859-1 message encoding"],
+  ])("rejects commits with the %s header", (header, message) => {
+    const raw = [
+      "tree aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+      "parent bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb",
+      "author Ada <ada@example.com> 1 +0000",
+      "committer Ada <ada@example.com> 1 +0000",
+      header,
+      "",
+      "Original message",
+      "",
+    ].join("\n");
+
+    expect(() =>
+      parseRawCommit("cccccccccccccccccccccccccccccccccccccccc", raw),
+    ).toThrow(message);
+  });
+
+  test("accepts an explicit UTF-8 encoding header", () => {
+    const raw = [
+      "tree aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+      "parent bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb",
+      "encoding UTF-8",
+      "",
+      "Original message",
+      "",
+    ].join("\n");
+
+    expect(
+      parseRawCommit("cccccccccccccccccccccccccccccccccccccccc", raw).message,
+    ).toBe("Original message\n");
+  });
+
   test("rewrites only the parent and message of a raw commit", () => {
     const raw = [
       "tree aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",