diff --git a/src/itsdangerous/timed.py b/src/itsdangerous/timed.py
index 52deeea..559064e 100644
--- a/src/itsdangerous/timed.py
+++ b/src/itsdangerous/timed.py
@@ -136,7 +136,7 @@ class TimestampSigner(Signer):
 
         # Check timestamp is not older than max_age
         if max_age is not None:
-            age = self.get_timestamp() - ts_int
+            age = ts_int - self.get_timestamp()
 
             if age > max_age:
                 raise SignatureExpired(