diff --git a/ofproto/ofproto-dpif-upcall.c b/ofproto/ofproto-dpif-upcall.c
index 7ad728adf..ad9635496 100644
--- a/ofproto/ofproto-dpif-upcall.c
+++ b/ofproto/ofproto-dpif-upcall.c
@@ -402,7 +402,8 @@ static int upcall_receive(struct upcall *, const struct dpif_backer *,
                           const struct dp_packet *packet, enum dpif_upcall_type,
                           const struct nlattr *userdata, const struct flow *,
                           const unsigned int mru,
-                          const ovs_u128 *ufid, const unsigned pmd_id);
+                          const ovs_u128 *ufid, const unsigned pmd_id,
+                          char **errorp);
 static void upcall_uninit(struct upcall *);
 
 static void udpif_flow_rebalance(struct udpif *udpif);
@@ -827,6 +828,7 @@ recv_upcalls(struct handler *handler)
         struct upcall *upcall = &upcalls[n_upcalls];
         struct flow *flow = &flows[n_upcalls];
         unsigned int mru = 0;
+        char *errorp = NULL;
         uint64_t hash = 0;
         int error;
 
@@ -853,7 +855,7 @@ recv_upcalls(struct handler *handler)
 
         error = upcall_receive(upcall, udpif->backer, &dupcall->packet,
                                dupcall->type, dupcall->userdata, flow, mru,
-                               &dupcall->ufid, PMD_ID_NULL);
+                               &dupcall->ufid, PMD_ID_NULL, &errorp);
         if (error) {
             if (error == ENODEV) {
                 /* Received packet on datapath port for which we couldn't
@@ -864,8 +866,11 @@ recv_upcalls(struct handler *handler)
                               dupcall->key_len, NULL, 0, NULL, 0,
                               &dupcall->ufid, PMD_ID_NULL, NULL);
                 VLOG_INFO_RL(&rl, "received packet on unassociated datapath "
-                             "port %"PRIu32, flow->in_port.odp_port);
+                             "port %"PRIu32"%s%s%s", flow->in_port.odp_port,
+                             errorp ? " (" : "", errorp ? errorp : "",
+                             errorp ? ")" : "");
             }
+            free(errorp);
             goto free_dupcall;
         }
 
@@ -1151,7 +1156,8 @@ upcall_receive(struct upcall *upcall, const struct dpif_backer *backer,
                const struct dp_packet *packet, enum dpif_upcall_type type,
                const struct nlattr *userdata, const struct flow *flow,
                const unsigned int mru,
-               const ovs_u128 *ufid, const unsigned pmd_id)
+               const ovs_u128 *ufid, const unsigned pmd_id,
+               char **errorp)
 {
     int error;
 
@@ -1160,7 +1166,8 @@ upcall_receive(struct upcall *upcall, const struct dpif_backer *backer,
         return EAGAIN;
     } else if (upcall->type == MISS_UPCALL) {
         error = xlate_lookup(backer, flow, &upcall->ofproto, &upcall->ipfix,
-                             &upcall->sflow, NULL, &upcall->ofp_in_port);
+                             &upcall->sflow, NULL, &upcall->ofp_in_port,
+                             errorp);
         if (error) {
             return error;
         }
@@ -1168,7 +1175,11 @@ upcall_receive(struct upcall *upcall, const struct dpif_backer *backer,
         struct ofproto_dpif *ofproto
             = ofproto_dpif_lookup_by_uuid(&upcall->cookie.ofproto_uuid);
         if (!ofproto) {
-            VLOG_INFO_RL(&rl, "upcall could not find ofproto");
+            if (errorp) {
+                *errorp = xstrdup("upcall could not find ofproto");
+            } else {
+                VLOG_INFO_RL(&rl, "upcall could not find ofproto");
+            }
             return ENODEV;
         }
         upcall->ofproto = ofproto;
@@ -1358,7 +1369,7 @@ upcall_cb(const struct dp_packet *packet, const struct flow *flow, ovs_u128 *ufi
     atomic_read_relaxed(&enable_megaflows, &megaflow);
 
     error = upcall_receive(&upcall, udpif->backer, packet, type, userdata,
-                           flow, 0, ufid, pmd_id);
+                           flow, 0, ufid, pmd_id, NULL);
     if (error) {
         return error;
     }
@@ -2154,7 +2165,7 @@ xlate_key(struct udpif *udpif, const struct nlattr *key, unsigned int len,
     }
 
     error = xlate_lookup(udpif->backer, &ctx->flow, &ofproto, NULL, NULL,
-                         ctx->netflow, &ofp_in_port);
+                         ctx->netflow, &ofp_in_port, NULL);
     if (error) {
         return error;
     }
diff --git a/ofproto/ofproto-dpif-xlate.c b/ofproto/ofproto-dpif-xlate.c
index ab6f39bb2..3b9b26da1 100644
--- a/ofproto/ofproto-dpif-xlate.c
+++ b/ofproto/ofproto-dpif-xlate.c
@@ -1603,17 +1603,19 @@ xlate_lookup_ofproto(const struct dpif_backer *backer, const struct flow *flow,
  * be taken.
  *
  * Returns 0 if successful, ENODEV if the parsed flow has no associated ofproto.
+ * Sets an extended error string to 'errorp'.  Callers are responsible for
+ * freeing that string.
  */
 int
 xlate_lookup(const struct dpif_backer *backer, const struct flow *flow,
              struct ofproto_dpif **ofprotop, struct dpif_ipfix **ipfix,
              struct dpif_sflow **sflow, struct netflow **netflow,
-             ofp_port_t *ofp_in_port)
+             ofp_port_t *ofp_in_port, char **errorp)
 {
     struct ofproto_dpif *ofproto;
     const struct xport *xport;
 
-    ofproto = xlate_lookup_ofproto_(backer, flow, ofp_in_port, &xport, NULL);
+    ofproto = xlate_lookup_ofproto_(backer, flow, ofp_in_port, &xport, errorp);
 
     if (!ofproto) {
         return ENODEV;
diff --git a/ofproto/ofproto-dpif-xlate.h b/ofproto/ofproto-dpif-xlate.h
index c1af477c4..05b46fb26 100644
--- a/ofproto/ofproto-dpif-xlate.h
+++ b/ofproto/ofproto-dpif-xlate.h
@@ -209,7 +209,7 @@ struct ofproto_dpif * xlate_lookup_ofproto(const struct dpif_backer *,
 int xlate_lookup(const struct dpif_backer *, const struct flow *,
                  struct ofproto_dpif **, struct dpif_ipfix **,
                  struct dpif_sflow **, struct netflow **,
-                 ofp_port_t *ofp_in_port);
+                 ofp_port_t *ofp_in_port, char **errorp);
 
 const char *xlate_strerror(enum xlate_error error);