diff --git a/share/man/man9/counter.9 b/share/man/man9/counter.9
index 8f77ce62e11..c29c475e733 100644
--- a/share/man/man9/counter.9
+++ b/share/man/man9/counter.9
@@ -33,6 +33,7 @@
 .Nd "SMP-friendly kernel counter implementation"
 .Sh SYNOPSIS
 .In sys/types.h
+.In sys/systm.h
 .In sys/counter.h
 .Ft counter_u64_t
 .Fn counter_u64_alloc "int wait"