diff --git a/changelog.d/11542.misc b/changelog.d/11542.misc
new file mode 100644
index 000000000000..f61416503766
--- /dev/null
+++ b/changelog.d/11542.misc
@@ -0,0 +1 @@
+Add missing `errcode` to `parse_string` and `parse_boolean`.
\ No newline at end of file
diff --git a/synapse/http/servlet.py b/synapse/http/servlet.py
index 6dd9b9ad0358..1627225f286d 100644
--- a/synapse/http/servlet.py
+++ b/synapse/http/servlet.py
@@ -246,7 +246,7 @@ def parse_boolean_from_args(
             message = (
                 "Boolean query parameter %r must be one of ['true', 'false']"
             ) % (name,)
-            raise SynapseError(400, message)
+            raise SynapseError(400, message, errcode=Codes.INVALID_PARAM)
     else:
         if required:
             message = "Missing boolean query parameter %r" % (name,)
@@ -414,7 +414,7 @@ def _parse_string_value(
             name,
             ", ".join(repr(v) for v in allowed_values),
         )
-        raise SynapseError(400, message)
+        raise SynapseError(400, message, errcode=Codes.INVALID_PARAM)
     else:
         return value_str
 
diff --git a/tests/rest/admin/test_federation.py b/tests/rest/admin/test_federation.py
index 5188499ef2d6..d1cd5b075157 100644
--- a/tests/rest/admin/test_federation.py
+++ b/tests/rest/admin/test_federation.py
@@ -95,7 +95,7 @@ def test_invalid_parameter(self):
         )
 
         self.assertEqual(HTTPStatus.BAD_REQUEST, channel.code, msg=channel.json_body)
-        self.assertEqual(Codes.UNKNOWN, channel.json_body["errcode"])
+        self.assertEqual(Codes.INVALID_PARAM, channel.json_body["errcode"])
 
         # invalid search order
         channel = self.make_request(
@@ -105,7 +105,7 @@ def test_invalid_parameter(self):
         )
 
         self.assertEqual(HTTPStatus.BAD_REQUEST, channel.code, msg=channel.json_body)
-        self.assertEqual(Codes.UNKNOWN, channel.json_body["errcode"])
+        self.assertEqual(Codes.INVALID_PARAM, channel.json_body["errcode"])
 
         # invalid destination
         channel = self.make_request(
diff --git a/tests/rest/admin/test_media.py b/tests/rest/admin/test_media.py
index 81e578fd26c1..3f727788cec8 100644
--- a/tests/rest/admin/test_media.py
+++ b/tests/rest/admin/test_media.py
@@ -360,7 +360,7 @@ def test_invalid_parameter(self) -> None:
             channel.code,
             msg=channel.json_body,
         )
-        self.assertEqual(Codes.UNKNOWN, channel.json_body["errcode"])
+        self.assertEqual(Codes.INVALID_PARAM, channel.json_body["errcode"])
         self.assertEqual(
             "Boolean query parameter 'keep_profiles' must be one of ['true', 'false']",
             channel.json_body["error"],
diff --git a/tests/rest/admin/test_statistics.py b/tests/rest/admin/test_statistics.py
index f6e85fdaadcd..7cb8ec57bad9 100644
--- a/tests/rest/admin/test_statistics.py
+++ b/tests/rest/admin/test_statistics.py
@@ -92,7 +92,7 @@ def test_invalid_parameter(self) -> None:
             channel.code,
             msg=channel.json_body,
         )
-        self.assertEqual(Codes.UNKNOWN, channel.json_body["errcode"])
+        self.assertEqual(Codes.INVALID_PARAM, channel.json_body["errcode"])
 
         # negative from
         channel = self.make_request(
diff --git a/tests/rest/admin/test_user.py b/tests/rest/admin/test_user.py
index 4fedd5fd0851..294d429ce12b 100644
--- a/tests/rest/admin/test_user.py
+++ b/tests/rest/admin/test_user.py
@@ -608,7 +608,7 @@ def test_invalid_parameter(self):
         )
 
         self.assertEqual(HTTPStatus.BAD_REQUEST, channel.code, msg=channel.json_body)
-        self.assertEqual(Codes.UNKNOWN, channel.json_body["errcode"])
+        self.assertEqual(Codes.INVALID_PARAM, channel.json_body["errcode"])
 
         # invalid deactivated
         channel = self.make_request(
@@ -618,7 +618,7 @@ def test_invalid_parameter(self):
         )
 
         self.assertEqual(HTTPStatus.BAD_REQUEST, channel.code, msg=channel.json_body)
-        self.assertEqual(Codes.UNKNOWN, channel.json_body["errcode"])
+        self.assertEqual(Codes.INVALID_PARAM, channel.json_body["errcode"])
 
         # unkown order_by
         channel = self.make_request(
@@ -628,7 +628,7 @@ def test_invalid_parameter(self):
         )
 
         self.assertEqual(HTTPStatus.BAD_REQUEST, channel.code, msg=channel.json_body)
-        self.assertEqual(Codes.UNKNOWN, channel.json_body["errcode"])
+        self.assertEqual(Codes.INVALID_PARAM, channel.json_body["errcode"])
 
         # invalid search order
         channel = self.make_request(
@@ -638,7 +638,7 @@ def test_invalid_parameter(self):
         )
 
         self.assertEqual(HTTPStatus.BAD_REQUEST, channel.code, msg=channel.json_body)
-        self.assertEqual(Codes.UNKNOWN, channel.json_body["errcode"])
+        self.assertEqual(Codes.INVALID_PARAM, channel.json_body["errcode"])
 
     def test_limit(self):
         """
@@ -2896,7 +2896,7 @@ def test_invalid_parameter(self, method: str):
         )
 
         self.assertEqual(HTTPStatus.BAD_REQUEST, channel.code, msg=channel.json_body)
-        self.assertEqual(Codes.UNKNOWN, channel.json_body["errcode"])
+        self.assertEqual(Codes.INVALID_PARAM, channel.json_body["errcode"])
 
         # invalid search order
         channel = self.make_request(
@@ -2906,7 +2906,7 @@ def test_invalid_parameter(self, method: str):
         )
 
         self.assertEqual(HTTPStatus.BAD_REQUEST, channel.code, msg=channel.json_body)
-        self.assertEqual(Codes.UNKNOWN, channel.json_body["errcode"])
+        self.assertEqual(Codes.INVALID_PARAM, channel.json_body["errcode"])
 
         # negative limit
         channel = self.make_request(