diff --git a/internal/wire/version_negotiation.go b/internal/wire/version_negotiation.go
index f605e15fb..4a6b323fa 100644
--- a/internal/wire/version_negotiation.go
+++ b/internal/wire/version_negotiation.go
@@ -11,7 +11,7 @@ import (
 // ComposeVersionNegotiation composes a Version Negotiation
 func ComposeVersionNegotiation(destConnID, srcConnID protocol.ConnectionID, versions []protocol.VersionNumber) ([]byte, error) {
 	greasedVersions := protocol.GetGreasedVersions(versions)
-	expectedLen := 1 /* type byte */ + 4 /* version field */ + 1 /* connection ID length field */ + destConnID.Len() + srcConnID.Len() + len(greasedVersions)*4
+	expectedLen := 1 /* type byte */ + 4 /* version field */ + 1 /* dest connection ID length field */ + destConnID.Len() + 1 /* src connection ID length field */ + srcConnID.Len() + len(greasedVersions)*4
 	buf := bytes.NewBuffer(make([]byte, 0, expectedLen))
 	r := make([]byte, 1)
 	_, _ = rand.Read(r) // ignore the error here. It is not critical to have perfect random here.