diff --git a/src/github/api/queries/github.ts b/src/github/api/queries/github.ts
index 1702061f..a6e8a185 100644
--- a/src/github/api/queries/github.ts
+++ b/src/github/api/queries/github.ts
@@ -84,6 +84,7 @@ export const PR_QUERY = `
                 body
                 path
                 line
+                diffHunk
                 author {
                   login
                 }
diff --git a/src/github/data/formatter.ts b/src/github/data/formatter.ts
index 82dbe568..ad428ebe 100644
--- a/src/github/data/formatter.ts
+++ b/src/github/data/formatter.ts
@@ -118,7 +118,16 @@ export function formatReviewComments(
 
           body = sanitizeContent(body);
 
-          return `  [Comment on ${comment.path}:${comment.line || "?"}]: ${body}`;
+          let formatted = `  [Comment on ${comment.path}:${comment.line || "?"}]: ${body}`;
+
+          // The diff hunk is the code the comment was left on. Without it the
+          // comment arrives without the context it was written against.
+          if (comment.diffHunk) {
+            const diffHunk = sanitizeContent(comment.diffHunk);
+            formatted += `\n  Diff context:\n\`\`\`diff\n${diffHunk}\n\`\`\``;
+          }
+
+          return formatted;
         })
         .join("\n");
       if (comments) {
diff --git a/src/github/types.ts b/src/github/types.ts
index d5053f42..c5140c12 100644
--- a/src/github/types.ts
+++ b/src/github/types.ts
@@ -22,6 +22,7 @@ export type GitHubComment = {
 export type GitHubReviewComment = GitHubComment & {
   path: string;
   line: number | null;
+  diffHunk?: string | null;
 };
 
 export type GitHubCommit = {
diff --git a/test/data-formatter.test.ts b/test/data-formatter.test.ts
index 423bbcda..8735f23e 100644
--- a/test/data-formatter.test.ts
+++ b/test/data-formatter.test.ts
@@ -508,6 +508,112 @@ describe("formatReviewComments", () => {
     );
   });
 
+  test("includes the diff hunk as context when present", () => {
+    const reviewData = {
+      nodes: [
+        {
+          id: "review1",
+          databaseId: "300001",
+          author: { login: "reviewer1" },
+          body: "",
+          state: "COMMENTED",
+          submittedAt: "2023-01-01T00:00:00Z",
+          comments: {
+            nodes: [
+              {
+                id: "comment1",
+                databaseId: "200001",
+                body: "This can overflow",
+                author: { login: "reviewer1" },
+                createdAt: "2023-01-01T00:00:00Z",
+                path: "src/index.ts",
+                line: 42,
+                diffHunk: "@@ -40,3 +40,3 @@\n-const a = 1;\n+const a = 2;",
+              },
+            ],
+          },
+        },
+      ],
+    };
+
+    const result = formatReviewComments(reviewData);
+
+    expect(result).toContain("[Comment on src/index.ts:42]: This can overflow");
+    expect(result).toContain("Diff context:");
+    expect(result).toContain("@@ -40,3 +40,3 @@");
+    expect(result).toContain("+const a = 2;");
+  });
+
+  test("omits the diff context when the comment has no diff hunk", () => {
+    const reviewData = {
+      nodes: [
+        {
+          id: "review1",
+          databaseId: "300001",
+          author: { login: "reviewer1" },
+          body: "",
+          state: "COMMENTED",
+          submittedAt: "2023-01-01T00:00:00Z",
+          comments: {
+            nodes: [
+              {
+                id: "comment1",
+                databaseId: "200001",
+                body: "No hunk here",
+                author: { login: "reviewer1" },
+                createdAt: "2023-01-01T00:00:00Z",
+                path: "src/index.ts",
+                line: 42,
+              },
+            ],
+          },
+        },
+      ],
+    };
+
+    const result = formatReviewComments(reviewData);
+
+    expect(result).toContain("[Comment on src/index.ts:42]: No hunk here");
+    expect(result).not.toContain("Diff context:");
+  });
+
+  // GitHub returns line: null and diffHunk: "" for outdated comments whose
+  // line no longer exists in the diff (observed on anthropics/claude-code-action#1025).
+  test("omits the diff context for an outdated comment with an empty diff hunk", () => {
+    const reviewData = {
+      nodes: [
+        {
+          id: "review1",
+          databaseId: "300001",
+          author: { login: "reviewer1" },
+          body: "",
+          state: "COMMENTED",
+          submittedAt: "2023-01-01T00:00:00Z",
+          comments: {
+            nodes: [
+              {
+                id: "comment1",
+                databaseId: "200001",
+                body: "Outdated comment",
+                author: { login: "reviewer1" },
+                createdAt: "2023-01-01T00:00:00Z",
+                path: "src/index.ts",
+                line: null,
+                diffHunk: "",
+              },
+            ],
+          },
+        },
+      ],
+    };
+
+    const result = formatReviewComments(reviewData);
+
+    expect(result).toContain("[Comment on src/index.ts:?]: Outdated comment");
+    expect(result).not.toContain("Diff context:");
+    expect(result).not.toContain("```diff");
+  });
+
   test("formats review with only body (no comments) correctly", () => {
     const reviewData = {
       nodes: [