diff --git a/docs/api.rst b/docs/api.rst
index 9378fa49..0f5b9f43 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -159,11 +159,11 @@ Exceptions
 
 .. class:: InvalidIssuedAtError
 
-    Raised when a token's ``iat`` claim is in the future
+    Raised when a token's ``iat`` claim is non-numeric
 
 .. class:: ImmatureSignatureError
 
-    Raised when a token's ``nbf`` claim represents a time in the future
+    Raised when a token's ``nbf`` or ``iat`` claims represent a time in the future
 
 .. class:: InvalidKeyError