diff --git a/packet_packer.go b/packet_packer.go
index ebaaa44a..a39a5a3a 100644
--- a/packet_packer.go
+++ b/packet_packer.go
@@ -366,8 +366,9 @@ func (p *packetPacker) writeAndSealPacket(
 			buffer.Write(bytes.Repeat([]byte{0}, paddingLen))
 		}
 	}
-	if protocol.ByteCount(buffer.Len()+sealer.Overhead()) > protocol.MaxPacketSize {
-		return nil, errors.New("PacketPacker BUG: packet too large")
+
+	if size := protocol.ByteCount(buffer.Len() + sealer.Overhead()); size > protocol.MaxPacketSize {
+		return nil, fmt.Errorf("PacketPacker BUG: packet too large (%d bytes, allowed %d bytes)", size, protocol.MaxPacketSize)
 	}
 
 	raw = raw[0:buffer.Len()]
diff --git a/packet_packer_test.go b/packet_packer_test.go
index 537a2937..034ed8fe 100644
--- a/packet_packer_test.go
+++ b/packet_packer_test.go
@@ -679,7 +679,8 @@ var _ = Describe("Packet packer", func() {
 				},
 			}
 			_, err := packer.PackHandshakeRetransmission(packet)
-			Expect(err).To(MatchError("PacketPacker BUG: packet too large"))
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(ContainSubstring("PacketPacker BUG: packet too large"))
 		})
 
 		It("pads Initial packets to the required minimum packet size", func() {