diff --git a/sys/netinet/in_pcb.c b/sys/netinet/in_pcb.c
--- a/sys/netinet/in_pcb.c
+++ b/sys/netinet/in_pcb.c
@@ -412,7 +412,7 @@
 			if (ratecheck(&lastprint, &interval))
 				printf("lb group port %d, limit reached\n",
 				    ntohs(grp->il_lport));
-			return (0);
+			return (ENOBUFS);
 		}
 
 		/* Expand this local group. */
diff --git a/tests/sys/netinet/so_reuseport_lb_test.c b/tests/sys/netinet/so_reuseport_lb_test.c
--- a/tests/sys/netinet/so_reuseport_lb_test.c
+++ b/tests/sys/netinet/so_reuseport_lb_test.c
@@ -238,10 +238,58 @@
 	}
 }
 
+/*
+ * Check that the kernel enforces a limit on the LB group size.  Currently that
+ * limit is 256 but it's not exported anywhere, so we have to hard-code that.
+ */
+ATF_TC_WITHOUT_HEAD(group_limit);
+ATF_TC_BODY(group_limit, tc)
+{
+	const int max = 256 + 1;
+	struct sockaddr_in addr;
+	socklen_t slen;
+	int error, *sds;
+	uint16_t port;
+
+	sds = calloc(max, sizeof(int));
+	ATF_REQUIRE_MSG(sds != NULL, "calloc() failed: %s", strerror(errno));
+
+	for (int i = 0; i < max; i++)
+		sds[i] = lb_listen_socket(PF_INET, 0);
+
+	port = htons(0);
+	for (int i = 0; i < max; i++) {
+		memset(&addr, 0, sizeof(addr));
+		addr.sin_len = sizeof(addr);
+		addr.sin_family = AF_INET;
+		addr.sin_port = port;
+		addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+
+		slen = sizeof(addr);
+		error = bind(sds[i], (const struct sockaddr *)&addr, slen);
+		if (i < max - 1) {
+			ATF_REQUIRE_MSG(error == 0, "bind() failed: %s",
+			    strerror(errno));
+			if (i == 0) {
+				memset(&addr, 0, sizeof(addr));
+				error = getsockname(sds[0],
+				    (struct sockaddr *)&addr, &slen);
+				ATF_REQUIRE_MSG(error == 0,
+				    "getsockname() failed: %s",
+				    strerror(errno));
+				port = addr.sin_port;
+			}
+		} else {
+			ATF_REQUIRE_ERRNO(EAGAIN, error == -1);
+		}
+	}
+}
+
 ATF_TP_ADD_TCS(tp)
 {
 	ATF_TP_ADD_TC(tp, basic_ipv4);
 	ATF_TP_ADD_TC(tp, basic_ipv6);
+	ATF_TP_ADD_TC(tp, group_limit);
 
 	return (atf_no_error());
 }