diff --git a/.changeset/update-pr-draft-only.md b/.changeset/update-pr-draft-only.md
new file mode 100644
index 0000000..666f2d3
--- /dev/null
+++ b/.changeset/update-pr-draft-only.md
@@ -0,0 +1,5 @@
+---
+'@github-tools/sdk': patch
+---
+
+Skip the REST update when `updatePullRequest` is called with only `draft`. Octokit was sending an empty PATCH body (`''`), which GitHub rejects with 400 before the GraphQL draft mutation could run.
diff --git a/packages/github-tools/src/core/pull-requests.ts b/packages/github-tools/src/core/pull-requests.ts
index f7b5efe..8bcb1f6 100644
--- a/packages/github-tools/src/core/pull-requests.ts
+++ b/packages/github-tools/src/core/pull-requests.ts
@@ -128,7 +128,10 @@ export const updatePullRequestDescription = 'Update a pull request — title, bo
 /** Not idempotent — each call applies a new revision. */
 export async function updatePullRequestCore({ token, owner, repo, pullNumber, title, body, state, base, draft }: { token: string, owner: string, repo: string, pullNumber: number, title?: string, body?: string, state?: 'open' | 'closed', base?: string, draft?: boolean }) {
   const octokit = createOctokit(token)
-  const { data } = await octokit.rest.pulls.update({ owner, repo, pull_number: pullNumber, title, body, state, base })
+  const hasRestUpdate = title !== undefined || body !== undefined || state !== undefined || base !== undefined
+  const { data } = hasRestUpdate
+    ? await octokit.rest.pulls.update({ owner, repo, pull_number: pullNumber, title, body, state, base })
+    : await octokit.rest.pulls.get({ owner, repo, pull_number: pullNumber })
 
   if (draft !== undefined && draft !== data.draft) {
     await octokit.graphql(draft ? CONVERT_TO_DRAFT_MUTATION : MARK_READY_FOR_REVIEW_MUTATION, { pullRequestId: data.node_id })
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 9075f2a..4830854 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -7,6 +7,7 @@ settings:
 overrides:
   '@ai-sdk/vue>ai': 7.0.70
   '@ai-sdk/workflow>ai': 7.0.70
+  undici@5: 6.28.0
 
 importers:
 
@@ -1589,10 +1590,6 @@ packages:
   '@fastify/accept-negotiator@2.0.1':
     resolution: {integrity: sha512-/c/TW2bO/v9JeEgoD/g1G5GxGeCF1Hafdf79WPmUlgYiBXummY0oX3VVq4yFkKKVBKDNlaDUYoab7g38RpPqCQ==}
 
-  '@fastify/busboy@2.1.1':
-    resolution: {integrity: sha512-vBZP4NlzfOlerQTnba4aqZoMhE/a9HY7HRqoOPaETQcSQuWEIyZMHGfVu6w9wGtGK5fED5qRs2DteVCjOH60sA==}
-    engines: {node: '>=14'}
-
   '@fingerprintjs/botd@2.0.0':
     resolution: {integrity: sha512-yhuz23NKEcBDTHmGz/ULrXlGnbHenO+xZmVwuBkuqHUkqvaZ5TAA0kAgcRy4Wyo5dIBdkIf57UXX8/c9UlMLJg==}
 
@@ -11110,10 +11107,6 @@ packages:
   undici-types@8.3.0:
     resolution: {integrity: sha512-j375ScV60dom+YkPFIfTLcOiPxkN/buHz5GobjLhixFuANaNs3C9l4GmrWqejgXWJ7BbJcFYpTEUkS1Ge8bpZQ==}
 
-  undici@5.29.0:
-    resolution: {integrity: sha512-raqeBD6NQK4SkWhQzeYKd1KmIG6dllBOTt55Rmkt4HtI9mwdWtJljnrXjAFUBLTSN67HWrOIZ3EPF4kjUw80Bg==}
-    engines: {node: '>=14.0'}
-
   undici@6.28.0:
     resolution: {integrity: sha512-LIY910g9TI13YS95lrMFrs8Rm/u/irgHeTWoKCoteeJ04CUJ92eEfj0rVn+7VKMPBpUPiUoBKfhNyLI23EE/KA==}
     engines: {node: '>=18.17'}
@@ -12131,7 +12124,7 @@ snapshots:
       '@ai-sdk/provider': 3.0.14
       '@standard-schema/spec': 1.1.0
       eventsource-parser: 3.1.0
-      undici: 5.29.0
+      undici: 6.28.0
       zod: 4.3.6
     optional: true
 
@@ -12140,7 +12133,7 @@ snapshots:
       '@ai-sdk/provider': 3.0.14
       '@standard-schema/spec': 1.1.0
       eventsource-parser: 3.1.0
-      undici: 5.29.0
+      undici: 6.28.0
       zod: 4.4.3
 
   '@ai-sdk/provider-utils@5.0.21(zod@4.4.3)':
@@ -13289,8 +13282,6 @@ snapshots:
   '@fastify/accept-negotiator@2.0.1':
     optional: true
 
-  '@fastify/busboy@2.1.1': {}
-
   '@fingerprintjs/botd@2.0.0': {}
 
   '@floating-ui/core@1.8.0':
@@ -26278,10 +26269,6 @@ snapshots:
 
   undici-types@8.3.0: {}
 
-  undici@5.29.0:
-    dependencies:
-      '@fastify/busboy': 2.1.1
-
   undici@6.28.0: {}
 
   undici@7.26.0: {}
diff --git a/pnpm-workspace.yaml b/pnpm-workspace.yaml
index 5e25354..0ef5e01 100644
--- a/pnpm-workspace.yaml
+++ b/pnpm-workspace.yaml
@@ -35,4 +35,5 @@ minimumReleaseAgeExclude:
 overrides:
   '@ai-sdk/vue>ai': 7.0.70
   '@ai-sdk/workflow>ai': 7.0.70
+  'undici@5': 6.28.0