diff --git a/src/unix/internal.h b/src/unix/internal.h
index 101dc745..31db5e29 100644
--- a/src/unix/internal.h
+++ b/src/unix/internal.h
@@ -55,6 +55,9 @@
 #define ACCESS_ONCE(type, var)                                                \
   (*(volatile type*) &(var))
 
+#define ROUND_UP(a, b)                                                        \
+  ((a) % (b) ? ((a) + (b)) - ((a) % (b)) : (a))
+
 #define UNREACHABLE()                                                         \
   do {                                                                        \
     assert(0 && "unreachable code");                                          \
diff --git a/src/unix/stream.c b/src/unix/stream.c
index ab9636d8..e721aa1d 100644
--- a/src/unix/stream.c
+++ b/src/unix/stream.c
@@ -301,7 +301,7 @@ int uv__stream_try_select(uv_stream_t* stream, int* fd) {
   if (fds[1] > max_fd)
     max_fd = fds[1];
 
-  sread_sz = (max_fd + NBBY) / NBBY;
+  sread_sz = ROUND_UP(max_fd + 1, sizeof(uint32_t) * NBBY) / NBBY;
   swrite_sz = sread_sz;
 
   s = uv__malloc(sizeof(*s) + sread_sz + swrite_sz);