diff --git a/bson/json_util.py b/bson/json_util.py
index 6f32683b17..82c0653934 100644
--- a/bson/json_util.py
+++ b/bson/json_util.py
@@ -775,9 +775,9 @@ def _parse_canonical_minkey(doc: Any, dummy0: Any) -> MinKey:
 def _parse_canonical_maxkey(doc: Any, dummy0: Any) -> MaxKey:
     """Decode a JSON MaxKey to bson.max_key.MaxKey."""
     if type(doc["$maxKey"]) is not int or doc["$maxKey"] != 1:
-        raise TypeError("$maxKey value must be 1: %s", (doc,))
+        raise TypeError(f"$maxKey value must be 1: {doc}")
     if len(doc) != 1:
-        raise TypeError(f"Bad $minKey, extra field(s): {doc}")
+        raise TypeError(f"Bad $maxKey, extra field(s): {doc}")
     return MaxKey()
 
 
diff --git a/test/test_json_util.py b/test/test_json_util.py
index fadcb431f6..195f1beac5 100644
--- a/test/test_json_util.py
+++ b/test/test_json_util.py
@@ -400,6 +400,13 @@ def test_minkey(self):
     def test_maxkey(self):
         self.round_trip({"m": MaxKey()})
 
+    def test_minkey_maxkey_errors(self):
+        for key in ("$minKey", "$maxKey"):
+            with self.assertRaisesRegex(TypeError, rf"^\{key} value must be 1: "):
+                json_util.loads(json.dumps({key: 2}))
+            with self.assertRaisesRegex(TypeError, rf"^Bad \{key}, extra field\(s\): "):
+                json_util.loads(json.dumps({key: 1, "x": 1}))
+
     def test_timestamp(self):
         dct = {"ts": Timestamp(4, 13)}
         res = json_util.dumps(dct, default=json_util.default)