diff --git a/src/github/schemas.ts b/src/github/schemas.ts
index 213458eb..83bf3736 100644
--- a/src/github/schemas.ts
+++ b/src/github/schemas.ts
@@ -281,7 +281,7 @@ export const GitHubPullRequestSchema = z.object({
   updated_at: z.string(),
   closed_at: z.string().nullable(),
   merged_at: z.string().nullable(),
-  merge_commit_sha: z.string(),
+  merge_commit_sha: z.string().nullable(),
   assignee: GitHubIssueAssigneeSchema.nullable(),
   assignees: z.array(GitHubIssueAssigneeSchema),
   head: GitHubPullRequestHeadSchema,
@@ -375,4 +375,4 @@ export type CreateIssueOptions = z.infer<typeof CreateIssueOptionsSchema>;
 export type CreatePullRequestOptions = z.infer<typeof CreatePullRequestOptionsSchema>;
 export type CreateBranchOptions = z.infer<typeof CreateBranchOptionsSchema>;
 export type GitHubCreateUpdateFileResponse = z.infer<typeof GitHubCreateUpdateFileResponseSchema>;
-export type GitHubSearchResponse = z.infer<typeof GitHubSearchResponseSchema>;
\ No newline at end of file
+export type GitHubSearchResponse = z.infer<typeof GitHubSearchResponseSchema>;