diff --git a/sys/netpfil/pf/pf.c b/sys/netpfil/pf/pf.c
index af81d39cd8ca..dd6461021e59 100644
--- a/sys/netpfil/pf/pf.c
+++ b/sys/netpfil/pf/pf.c
@@ -915,7 +915,7 @@ pf_state_key_attach(struct pf_state_key *skw, struct pf_state_key *sks,
 					uma_zfree(V_pf_state_key_z, sk);
 					if (idx == PF_SK_STACK)
 						pf_detach_state(s);
-					return (-1);	/* collision! */
+					return (EEXIST); /* collision! */
 				}
 			}
 			PF_HASHROW_UNLOCK(ih);
@@ -1072,6 +1072,7 @@ pf_state_insert(struct pfi_kif *kif, struct pf_state_key *skw,
 {
 	struct pf_idhash *ih;
 	struct pf_state *cur;
+	int error;
 
 	KASSERT(TAILQ_EMPTY(&sks->states[0]) && TAILQ_EMPTY(&sks->states[1]),
 	    ("%s: sks not pristine", __func__));
@@ -1090,8 +1091,8 @@ pf_state_insert(struct pfi_kif *kif, struct pf_state_key *skw,
 		s->creatorid = V_pf_status.hostid;
 	}
 
-	if (pf_state_key_attach(skw, sks, s))
-		return (-1);
+	if ((error = pf_state_key_attach(skw, sks, s)) != 0)
+		return (error);
 
 	ih = &V_pf_idhash[PF_IDHASH(s)];
 	PF_HASHROW_LOCK(ih);
@@ -1108,7 +1109,7 @@ pf_state_insert(struct pfi_kif *kif, struct pf_state_key *skw,
 			    ntohl(s->creatorid));
 		}
 		pf_detach_state(s);
-		return (-1);
+		return (EEXIST);
 	}
 	LIST_INSERT_HEAD(&ih->states, s, entry);
 	/* One for keys, one for ID hash. */