diff --git a/lib/libc/gen/setmode.3 b/lib/libc/gen/setmode.3
index 429ddb236c52..4a236b21164f 100644
--- a/lib/libc/gen/setmode.3
+++ b/lib/libc/gen/setmode.3
@@ -39,6 +39,7 @@
 .Nm setmode
 .Nd modify mode bits
 .Sh SYNOPSIS
+.Fd #include <unistd.h>
 .Ft mode_t
 .Fn getmode "const void *set" "mode_t mode"
 .Ft void *