diff --git a/sys/compat/linux/linux_mmap.c b/sys/compat/linux/linux_mmap.c
--- a/sys/compat/linux/linux_mmap.c
+++ b/sys/compat/linux/linux_mmap.c
@@ -230,7 +230,9 @@
 linux_mprotect_common(struct thread *td, uintptr_t addr, size_t len, int prot)
 {
 
-	/* XXX Ignore PROT_GROWSDOWN and PROT_GROWSUP for now. */
+	if ((prot & LINUX_PROT_GROWSDOWN) != 0)
+		addr -= len;
+	/* Clear PROT_GROWSDOWN and PROT_GROWSUP. */
 	prot &= ~(LINUX_PROT_GROWSDOWN | LINUX_PROT_GROWSUP);
 	if ((prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC)) != 0)
 		return (EINVAL);