1 files changed, 21 insertions, 5 deletions
diff --git a/synapse/config/captcha.py b/synapse/config/captcha.py
index 9e48f865cc..92c603f224 100644
--- a/synapse/config/captcha.py
+++ b/synapse/config/captcha.py
@@ -12,15 +12,31 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from ._base import Config
+from typing import Any
+
+from synapse.types import JsonDict
+
+from ._base import Config, ConfigError
 
 
 class CaptchaConfig(Config):
     section = "captcha"
 
-    def read_config(self, config, **kwargs):
-        self.recaptcha_private_key = config.get("recaptcha_private_key")
-        self.recaptcha_public_key = config.get("recaptcha_public_key")
+    def read_config(self, config: JsonDict, **kwargs: Any) -> None:
+        recaptcha_private_key = config.get("recaptcha_private_key")
+        if recaptcha_private_key is not None and not isinstance(
+            recaptcha_private_key, str
+        ):
+            raise ConfigError("recaptcha_private_key must be a string.")
+        self.recaptcha_private_key = recaptcha_private_key
+
+        recaptcha_public_key = config.get("recaptcha_public_key")
+        if recaptcha_public_key is not None and not isinstance(
+            recaptcha_public_key, str
+        ):
+            raise ConfigError("recaptcha_public_key must be a string.")
+        self.recaptcha_public_key = recaptcha_public_key
+
         self.enable_registration_captcha = config.get(
             "enable_registration_captcha", False
         )
@@ -30,7 +46,7 @@ class CaptchaConfig(Config):
         )
         self.recaptcha_template = self.read_template("recaptcha.html")
 
-    def generate_config_section(self, **kwargs):
+    def generate_config_section(self, **kwargs: Any) -> str:
         return """\
         ## Captcha ##
         # See docs/CAPTCHA_SETUP.md for full details of configuring this.