diff --git a/lib/netdev-native-tnl.c b/lib/netdev-native-tnl.c
index 74e89ba09ea..a9c950db3f3 100644
--- a/lib/netdev-native-tnl.c
+++ b/lib/netdev-native-tnl.c
@@ -61,6 +61,27 @@ static struct vlog_rate_limit err_rl = VLOG_RATE_LIMIT_INIT(60, 5);
 uint16_t tnl_udp_port_min = 32768;
 uint16_t tnl_udp_port_max = 61000;
 
+ovs_be16
+netdev_tnl_get_src_port(struct dp_packet *packet)
+{
+    uint32_t hash;
+
+    if (OVS_LIKELY(dp_packet_rss_valid(packet))) {
+        hash = dp_packet_get_rss_hash(packet);
+    } else {
+        struct flow flow;
+
+        flow_extract(packet, &flow);
+        hash = flow_hash_5tuple(&flow, 0);
+
+        dp_packet_set_rss_hash(packet, hash);
+    }
+
+    hash = ((uint64_t) hash * (tnl_udp_port_max - tnl_udp_port_min)) >> 32;
+
+    return htons(hash + tnl_udp_port_min);
+}
+
 void *
 netdev_tnl_ip_extract_tnl_md(struct dp_packet *packet, struct flow_tnl *tnl,
                   unsigned int *hlen)
@@ -276,14 +297,18 @@ netdev_tnl_push_udp_header(const struct netdev *netdev OVS_UNUSED,
     uint16_t l3_ofs = packet->l3_ofs;
     uint16_t l4_ofs = packet->l4_ofs;
     struct udp_header *udp;
+    ovs_be16 udp_src;
     int ip_tot_size;
 
+    /* We may need to re-calculate the hash and this has to be done before
+     * modifying the packet. */
+    udp_src = netdev_tnl_get_src_port(packet);
+
     dp_packet_tnl_ol_process(packet, data);
     udp = netdev_tnl_push_ip_header(packet, data->header, data->header_len,
                                     &ip_tot_size, 0);
 
-    /* set udp src port */
-    udp->udp_src = netdev_tnl_get_src_port(packet);
+    udp->udp_src = udp_src;
     udp->udp_len = htons(ip_tot_size);
 
     if (udp->udp_csum) {
@@ -831,13 +856,18 @@ netdev_gtpu_push_header(const struct netdev *netdev,
     struct netdev_vport *dev = netdev_vport_cast(netdev);
     struct udp_header *udp;
     struct gtpuhdr *gtpuh;
+    ovs_be16 udp_src;
     int ip_tot_size;
     unsigned int payload_len;
 
+    /* We may need to re-calculate the hash and this has to be done before
+     * modifying the packet. */
+    udp_src = netdev_tnl_get_src_port(packet);
+
     payload_len = dp_packet_size(packet);
     udp = netdev_tnl_push_ip_header(packet, data->header, data->header_len,
                                     &ip_tot_size, 0);
-    udp->udp_src = netdev_tnl_get_src_port(packet);
+    udp->udp_src = udp_src;
     udp->udp_len = htons(ip_tot_size);
     /* Postpone checksum to the egress netdev. */
     dp_packet_hwol_set_csum_udp(packet);
diff --git a/lib/netdev-native-tnl.h b/lib/netdev-native-tnl.h
index eb55dd0417a..5d8f1672a86 100644
--- a/lib/netdev-native-tnl.h
+++ b/lib/netdev-native-tnl.h
@@ -123,16 +123,7 @@ netdev_tnl_ip_build_header(struct ovs_action_push_tnl *data,
 extern uint16_t tnl_udp_port_min;
 extern uint16_t tnl_udp_port_max;
 
-static inline ovs_be16
-netdev_tnl_get_src_port(struct dp_packet *packet)
-{
-    uint32_t hash;
-
-    hash = dp_packet_get_rss_hash(packet);
-
-    return htons((((uint64_t) hash * (tnl_udp_port_max - tnl_udp_port_min)) >> 32) +
-                 tnl_udp_port_min);
-}
+ovs_be16 netdev_tnl_get_src_port(struct dp_packet *);
 
 void *
 netdev_tnl_ip_extract_tnl_md(struct dp_packet *packet, struct flow_tnl *tnl,
diff --git a/tests/tunnel-push-pop.at b/tests/tunnel-push-pop.at
index 885df07e5a6..061650860d1 100644
--- a/tests/tunnel-push-pop.at
+++ b/tests/tunnel-push-pop.at
@@ -767,6 +767,16 @@ dnl Sending again to exercise the non-miss upcall path.
 AT_CHECK([ovs-appctl netdev-dummy/receive int-br "${packet}4"])
 OVS_WAIT_UNTIL([test `ovs-pcap p0.pcap | grep -E "${encap}${packet}4" | wc -l` -ge 2])
 
+dnl Send two more packets at the same time to make sure they are distinct
+dnl memory buffers.
+AT_CHECK([ovs-appctl netdev-dummy/receive int-br "${packet}4" "${packet}4"])
+OVS_WAIT_UNTIL([test `ovs-pcap p0.pcap | grep -E "${encap}${packet}4" | wc -l` -ge 4])
+
+dnl Make sure all the packets are the same, i.e. have the same source port.
+AT_CHECK([ovs-pcap p0.pcap | sed 's/.$//' | sort | uniq \
+            | grep -E -c "${encap}${packet}"], [0], [1
+])
+
 dnl Output to tunnel from the controller.
 AT_CHECK([ovs-ofctl -O OpenFlow13 packet-out int-br CONTROLLER "debug_slow,output:2" "${packet}5"])
 OVS_WAIT_UNTIL([test `ovs-pcap p0.pcap | grep -E "${encap}${packet}5" | wc -l` -ge 1])