diff --git a/src/include/port/win32_msvc/unistd.h b/src/include/port/win32_msvc/unistd.h
index b63f4770a1..b7795ba03c 100644
--- a/src/include/port/win32_msvc/unistd.h
+++ b/src/include/port/win32_msvc/unistd.h
@@ -1 +1,9 @@
 /* src/include/port/win32_msvc/unistd.h */
+
+/*
+ * MSVC does not define these, nor does _fileno(stdin) etc reliably work
+ * (returns -1 if stdin/out/err are closed).
+ */
+#define STDIN_FILENO	0
+#define STDOUT_FILENO	1
+#define STDERR_FILENO	2