diff --git a/src/mem/packet.cc b/src/mem/packet.cc
index aefaf975d9..64f4fcd147 100644
--- a/src/mem/packet.cc
+++ b/src/mem/packet.cc
@@ -286,6 +286,7 @@ Packet::checkFunctional(Printable *obj, Addr addr, int size, uint8_t *data)
                           "for functional copying!");
                 }
             }
+            assert(bytesValidEnd <= getSize());
 
             // copy partial data into the packet's data array
             uint8_t *dest = getPtr<uint8_t>() + func_offset;