diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index 382fcdd49..33b3a503e 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -1305,6 +1305,11 @@ func (s *Stack) FindRoute(id tcpip.NICID, localAddr, remoteAddr tcpip.Address, n
 	s.mu.RLock()
 	defer s.mu.RUnlock()
 
+	// Reject attempts to use unsupported protocols.
+	if !s.CheckNetworkProtocol(netProto) {
+		return nil, &tcpip.ErrUnknownProtocol{}
+	}
+
 	isLinkLocal := header.IsV6LinkLocalUnicastAddress(remoteAddr) || header.IsV6LinkLocalMulticastAddress(remoteAddr)
 	isLocalBroadcast := remoteAddr == header.IPv4Broadcast
 	isMulticast := header.IsV4MulticastAddress(remoteAddr) || header.IsV6MulticastAddress(remoteAddr)