diff --git a/valkey/commands/core.py b/valkey/commands/core.py
index 481ac6d2..5e915bfc 100644
--- a/valkey/commands/core.py
+++ b/valkey/commands/core.py
@@ -2313,11 +2313,15 @@ def set(
             pieces.append("EXAT")
             if isinstance(exat, datetime.datetime):
                 exat = int(exat.timestamp())
+            elif not isinstance(exat, int):
+                raise DataError("exat must be of type datetime.datetime or int")
             pieces.append(exat)
         if pxat is not None:
             pieces.append("PXAT")
             if isinstance(pxat, datetime.datetime):
                 pxat = int(pxat.timestamp() * 1000)
+            elif not isinstance(pxat, int):
+                raise DataError("pxat must be of type datetime.datetime or int")
             pieces.append(pxat)
         if keepttl:
             pieces.append("KEEPTTL")