Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -1404,10 +1404,11 @@
 	AC_CHECK_HEADER(netinet/tcp.h, [
 		AC_DEFINE(OF_HAVE_NETINET_TCP_H, 1,
 			[Whether we have netinet/tcp.h])
 	])
 	AC_CHECK_HEADERS([arpa/inet.h netdb.h net/if.h])
+	AC_CHECK_FUNCS([if_indextoname if_nametoindex])
 	AC_CHECK_HEADER(sys/un.h, [
 		AC_DEFINE(OF_HAVE_SYS_UN_H, 1, [Whether we have sys/un.h])
 	])
 	AC_CHECK_MEMBER([struct sockaddr_in6.sin6_addr], [
 		AC_EGREP_CPP(egrep_cpp_yes, [

Index: src/OFSocket.m
==================================================================
--- src/OFSocket.m
+++ src/OFSocket.m
@@ -468,18 +468,20 @@
 	addrIn6->sin6_family = AF_UNSPEC;
 #endif
 	addrIn6->sin6_port = OFToBigEndian16(port);
 
 	if ((percent = [IPv6 rangeOfString: @"%"].location) != OFNotFound) {
+#if defined(HAVE_IF_NAMETOINDEX) || defined(OF_WINDOWS)
 		OFString *interface = [IPv6 substringFromIndex: percent + 1];
+#endif
 		IPv6 = [IPv6 substringToIndex: percent];
 
-#ifdef OF_WINDOWS
+#if defined(OF_WINDOWS)
 		if (if_nametoindexPtr != NULL)
 			addrIn6->sin6_scope_id = if_nametoindexPtr([interface
 			    cStringWithEncoding: [OFLocale encoding]]);
-#else
+#elif defined(HAVE_IF_NAMETOINDEX)
 		addrIn6->sin6_scope_id = if_nametoindex(
 		    [interface cStringWithEncoding: [OFLocale encoding]]);
 #endif
 	}
 
@@ -904,25 +906,27 @@
 			    addrIn6->sin6_addr.s6_addr[i + 1]];
 			first = false;
 		}
 	}
 
+#if defined(HAVE_IF_INDEXTONAME) || defined(OF_WINDOWS)
 	if (addrIn6->sin6_scope_id != 0) {
-#ifdef OF_WINDOWS
+# ifdef OF_WINDOWS
 		char interface[IF_MAX_STRING_SIZE];
 
 		if (if_indextonamePtr != NULL && if_indextonamePtr(
 		    addrIn6->sin6_scope_id, interface) != NULL)
-#else
+# else
 		char interface[IF_NAMESIZE];
 
 		if (if_indextoname(addrIn6->sin6_scope_id, interface) != NULL)
-#endif
+# endif
 			[string appendFormat: @"%%%s", interface];
 		else
 			[string appendFormat: @"%%%u", addrIn6->sin6_scope_id];
 	}
+#endif
 
 	[string makeImmutable];
 
 	return string;
 }