Index: head/lib/libnv/msgio.c
===================================================================
--- head/lib/libnv/msgio.c
+++ head/lib/libnv/msgio.c
@@ -63,7 +63,13 @@
 /* Linux: arbitrary size, but must be lower than SCM_MAX_FD. */
 #define	PKG_MAX_SIZE	((64U - 1) * CMSG_SPACE(sizeof(int)))
 #else
-#define	PKG_MAX_SIZE	(MCLBYTES / CMSG_SPACE(sizeof(int)) - 1)
+/*
+ * To work around limitations in 32-bit emulation on 64-bit kernels, use a
+ * machine-independent limit on the number of FDs per message.  Each control
+ * message contains 1 FD and requires 12 bytes for the header, 4 pad bytes,
+ * 4 bytes for the descriptor, and another 4 pad bytes.
+ */
+#define	PKG_MAX_SIZE	(MCLBYTES / 24)
 #endif
 
 static int