diff --git a/src/proto_tcp.c b/src/proto_tcp.c
index 3d56cf6..2f8ec22 100644
--- a/src/proto_tcp.c
+++ b/src/proto_tcp.c
@@ -681,6 +681,65 @@
 
 }
 
+/* Returns true if the passed FD corresponds to a socket bound with LI_O_FOREIGN
+ * according to the various supported socket options. The socket's address family
+ * must be passed in <family>.
+ */
+int tcp_is_foreign(int fd, sa_family_t family)
+{
+	int val __maybe_unused;
+	socklen_t len __maybe_unused;
+
+	switch (family) {
+	case AF_INET:
+#if defined(IP_TRANSPARENT)
+		val = 0; len = sizeof(val);
+		if (getsockopt(fd, SOL_IP, IP_TRANSPARENT, &val, &len) == 0 && val)
+			return 1;
+#endif
+#if defined(IP_FREEBIND)
+		val = 0; len = sizeof(val);
+		if (getsockopt(fd, SOL_IP, IP_FREEBIND, &val, &len) == 0 && val)
+			return 1;
+#endif
+#if defined(IP_BINDANY)
+		val = 0; len = sizeof(val);
+		if (getsockopt(fd, IPPROTO_IP, IP_BINDANY, &val, &len) == 0 && val)
+			return 1;
+#endif
+#if defined(SO_BINDANY)
+		val = 0; len = sizeof(val);
+		if (getsockopt(fd, SOL_SOCKET, SO_BINDANY, &val, &len) == 0 && val)
+			return 1;
+#endif
+		break;
+
+	case AF_INET6:
+#if defined(IPV6_TRANSPARENT) && defined(SOL_IPV6)
+		val = 0; len = sizeof(val);
+		if (getsockopt(fd, SOL_IPV6, IPV6_TRANSPARENT, &val, &len) == 0 && val)
+			return 1;
+#endif
+#if defined(IP_FREEBIND)
+		val = 0; len = sizeof(val);
+		if (getsockopt(fd, SOL_IP, IP_FREEBIND, &val, &len) == 0 && val)
+			return 1;
+#endif
+#if defined(IPV6_BINDANY)
+		val = 0; len = sizeof(val);
+		if (getsockopt(fd, IPPROTO_IPV6, IPV6_BINDANY, &val, &len) == 0 && val)
+			return 1;
+#endif
+#if defined(SO_BINDANY)
+		val = 0; len = sizeof(val);
+		if (getsockopt(fd, SOL_SOCKET, SO_BINDANY, &val, &len) == 0 && val)
+			return 1;
+#endif
+		break;
+	}
+	return 0;
+}
+
 /* sets the v6only_default flag according to the OS' default settings; for
  * simplicity it's set to zero if not supported.
  */