diff --git a/jsonschema/_format.py b/jsonschema/_format.py
index 9b4e67b6..318826ed 100644
--- a/jsonschema/_format.py
+++ b/jsonschema/_format.py
@@ -516,6 +516,9 @@ def is_duration(instance: object) -> bool:
 )
 def is_uuid(instance: object) -> bool:
     if not isinstance(instance, str):
-        return True
-    UUID(instance)
+        return False
+    try:
+        UUID(instance)
+    except:
+        return False
     return all(instance[position] == "-" for position in (8, 13, 18, 23))