diff --git a/bot_bottle/contrib/gitea/deploy_key_provisioner.py b/bot_bottle/contrib/gitea/deploy_key_provisioner.py
index 0ceadd7..9a4a9dc 100644
--- a/bot_bottle/contrib/gitea/deploy_key_provisioner.py
+++ b/bot_bottle/contrib/gitea/deploy_key_provisioner.py
@@ -19,7 +19,7 @@ import urllib.error
 import urllib.request
 from pathlib import Path
 
-from ...deploy_key_provisioner import DeployKeyProvisioner
+from ...deploy_key_provisioner import DeployKeyCollisionError, DeployKeyProvisioner
 
 
 class GiteaDeployKeyProvisioner(DeployKeyProvisioner):
@@ -71,6 +71,11 @@ class GiteaDeployKeyProvisioner(DeployKeyProvisioner):
                 body = json.loads(resp.read())
         except urllib.error.HTTPError as exc:
             _body = _read_error_body(exc)
+            if exc.code == 422:
+                raise DeployKeyCollisionError(
+                    f"deploy key collision for {owner_repo!r} "
+                    f"(title={title!r}): key title or content already registered — {_body}"
+                ) from exc
             raise RuntimeError(
                 f"failed to create deploy key for {owner_repo}: "
                 f"HTTP {exc.code} — {_body}"
diff --git a/bot_bottle/deploy_key_provisioner.py b/bot_bottle/deploy_key_provisioner.py
index b7cac3c..e733bc1 100644
--- a/bot_bottle/deploy_key_provisioner.py
+++ b/bot_bottle/deploy_key_provisioner.py
@@ -11,6 +11,10 @@ from __future__ import annotations
 from abc import ABC, abstractmethod
 
 
+class DeployKeyCollisionError(RuntimeError):
+    """Raised when a deploy key title or public key already exists on the repo."""
+
+
 class DeployKeyProvisioner(ABC):
     """Manages a single deploy-key lifecycle on a remote forge."""
 
diff --git a/tests/unit/test_contrib_gitea_deploy_key.py b/tests/unit/test_contrib_gitea_deploy_key.py
index b5a0402..469f757 100644
--- a/tests/unit/test_contrib_gitea_deploy_key.py
+++ b/tests/unit/test_contrib_gitea_deploy_key.py
@@ -12,6 +12,7 @@ from bot_bottle.contrib.gitea.deploy_key_provisioner import (
     GiteaDeployKeyProvisioner,
     _split_owner_repo,
 )
+from bot_bottle.deploy_key_provisioner import DeployKeyCollisionError
 
 
 def _provisioner() -> GiteaDeployKeyProvisioner:
@@ -100,6 +101,30 @@ class TestCreate(unittest.TestCase):
                 provisioner.create("owner/repo", "title")
         self.assertIn("403", str(ctx.exception))
 
+    def test_create_raises_collision_error_on_422(self):
+        provisioner = _provisioner()
+        collision_body = json.dumps({
+            "errors": ["Key content already exists on this repository"],
+            "message": "422 Unprocessable Entity",
+        })
+        with patch(
+            "bot_bottle.contrib.gitea.deploy_key_provisioner.subprocess.run"
+        ), patch(
+            "bot_bottle.contrib.gitea.deploy_key_provisioner.urllib.request.urlopen",
+            side_effect=_http_error(422, collision_body),
+        ), patch(
+            "bot_bottle.contrib.gitea.deploy_key_provisioner.Path.read_bytes",
+            return_value=b"pk",
+        ), patch(
+            "bot_bottle.contrib.gitea.deploy_key_provisioner.Path.read_text",
+            return_value="ssh-ed25519 AAAA\n",
+        ):
+            with self.assertRaises(DeployKeyCollisionError) as ctx:
+                provisioner.create("owner/repo", "my-title")
+        msg = str(ctx.exception)
+        self.assertIn("owner/repo", msg)
+        self.assertIn("my-title", msg)
+
 
 class TestDelete(unittest.TestCase):
     def test_delete_calls_correct_endpoint(self):