diff --git a/miner/block.go b/miner/block.go
index 4bf25a548c..9ce32063f4 100644
--- a/miner/block.go
+++ b/miner/block.go
@@ -384,7 +384,10 @@ func createConversionFunctions(sysCtx *core.SysContractCallCtx, chain *core.Bloc
 	}
 	toCeloFn := func(amount *big.Int, feeCurrency *common.Address) *big.Int {
 		curr, _ := currencyManager.GetCurrency(feeCurrency)
-		return curr.ToCELO(amount)
+		if curr != nil {
+			return curr.ToCELO(amount)
+		}
+		return nil
 	}
 
 	return baseFeeFn, toCeloFn
diff --git a/p2p/discover/v4_udp_test.go b/p2p/discover/v4_udp_test.go
index c5340a7a59..49e892f285 100644
--- a/p2p/discover/v4_udp_test.go
+++ b/p2p/discover/v4_udp_test.go
@@ -571,6 +571,8 @@ func startLocalhostV4(t *testing.T, cfg Config) *UDPv4 {
 	if err != nil {
 		t.Fatal(err)
 	}
+	defer socket.Close()
+	
 	realaddr := socket.LocalAddr().(*net.UDPAddr)
 	ln.SetStaticIP(realaddr.IP)
 	ln.SetFallbackUDP(realaddr.Port)
diff --git a/p2p/discover/v5_udp_test.go b/p2p/discover/v5_udp_test.go
index 12b9993767..b86ba322cd 100644
--- a/p2p/discover/v5_udp_test.go
+++ b/p2p/discover/v5_udp_test.go
@@ -90,6 +90,8 @@ func startLocalhostV5(t *testing.T, cfg Config) *UDPv5 {
 	if err != nil {
 		t.Fatal(err)
 	}
+	defer socket.Close()
+	
 	realaddr := socket.LocalAddr().(*net.UDPAddr)
 	ln.SetStaticIP(realaddr.IP)
 	ln.Set(enr.UDP(realaddr.Port))
diff --git a/p2p/server.go b/p2p/server.go
index c68f5d3667..801ae8f51b 100644
--- a/p2p/server.go
+++ b/p2p/server.go
@@ -660,6 +660,8 @@ func (srv *Server) setupDiscovery() error {
 	if err != nil {
 		return err
 	}
+	defer conn.Close()
+	
 	realaddr := conn.LocalAddr().(*net.UDPAddr)
 	srv.log.Debug("UDP listener up", "addr", realaddr)
 	if srv.NAT != nil {