diff --git a/repos/libports/src/lib/libc/socket_fs_plugin.cc b/repos/libports/src/lib/libc/socket_fs_plugin.cc
index 74ce0a61c2..ddeaf480a3 100644
--- a/repos/libports/src/lib/libc/socket_fs_plugin.cc
+++ b/repos/libports/src/lib/libc/socket_fs_plugin.cc
@@ -1222,13 +1222,19 @@ int Socket_fs::Plugin::select(int nfds,
 
 	for (int fd = 0; fd < nfds; ++fd) {
 
+		bool fd_in_readfds = FD_ISSET(fd, &in_readfds);
+		bool fd_in_writefds = FD_ISSET(fd, &in_writefds);
+
+		if (!fd_in_readfds && !fd_in_writefds)
+			continue;
+
 		File_descriptor *fdo = file_descriptor_allocator()->find_by_libc_fd(fd);
 
 		/* handle only fds that belong to this plugin */
 		if (!fdo || (fdo->plugin != this))
 			continue;
 
-		if (FD_ISSET(fd, &in_readfds)) {
+		if (fd_in_readfds) {
 			try {
 				Socket_fs::Context *context = dynamic_cast<Socket_fs::Context *>(fdo->context);
 
@@ -1239,7 +1245,7 @@ int Socket_fs::Plugin::select(int nfds,
 			} catch (Socket_fs::Context::Inaccessible) { }
 		}
 
-		if (FD_ISSET(fd, &in_writefds)) {
+		if (fd_in_writefds) {
 			try {
 				Socket_fs::Context *context = dynamic_cast<Socket_fs::Context *>(fdo->context);
 
diff --git a/repos/libports/src/lib/libc/vfs_plugin.cc b/repos/libports/src/lib/libc/vfs_plugin.cc
index 039d24f0f8..0711235b1f 100644
--- a/repos/libports/src/lib/libc/vfs_plugin.cc
+++ b/repos/libports/src/lib/libc/vfs_plugin.cc
@@ -2080,6 +2080,12 @@ int Libc::Vfs_plugin::select(int nfds,
 	auto fn = [&] {
 		for (int fd = 0; fd < nfds; ++fd) {
 
+			bool fd_in_readfds = FD_ISSET(fd, &in_readfds);
+			bool fd_in_writefds = FD_ISSET(fd, &in_writefds);
+
+			if (!fd_in_readfds && !fd_in_writefds)
+				continue;
+
 			File_descriptor *fdo =
 				file_descriptor_allocator()->find_by_libc_fd(fd);
 
@@ -2090,7 +2096,7 @@ int Libc::Vfs_plugin::select(int nfds,
 			Vfs::Vfs_handle *handle = vfs_handle(fdo);
 			if (!handle) continue;
 
-			if (FD_ISSET(fd, &in_readfds)) {
+			if (fd_in_readfds) {
 				if (handle->fs().read_ready(handle)) {
 					FD_SET(fd, readfds);
 					++nready;
@@ -2099,7 +2105,7 @@ int Libc::Vfs_plugin::select(int nfds,
 				}
 			}
 
-			if (FD_ISSET(fd, &in_writefds)) {
+			if (fd_in_writefds) {
 				if (true /* XXX always writeable */) {
 					FD_SET(fd, writefds);
 					++nready;