diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -1028,9 +1028,7 @@
 				goto fail2;
 			}
 		} else {
-			kasan_mark((void *)td2->td_kstack,
-			    ptoa(td2->td_kstack_pages),
-			    ptoa(td2->td_kstack_pages), 0);
+			kasan_kstack_unpoison(td2);
 		}
 	}
 
diff --git a/sys/kern/subr_asan.c b/sys/kern/subr_asan.c
--- a/sys/kern/subr_asan.c
+++ b/sys/kern/subr_asan.c
@@ -39,6 +39,7 @@
 #include <sys/systm.h>
 #include <sys/asan.h>
 #include <sys/kernel.h>
+#include <sys/proc.h>
 #include <sys/stack.h>
 #include <sys/sysctl.h>
 
@@ -429,6 +430,13 @@
 	}
 }
 
+void
+kasan_kstack_unpoison(struct thread *td)
+{
+	kasan_mark((void *)td->td_kstack, ptoa(td->td_kstack_pages),
+	    ptoa(td->td_kstack_pages), 0);
+}
+
 /* -------------------------------------------------------------------------- */
 
 void *
diff --git a/sys/sys/asan.h b/sys/sys/asan.h
--- a/sys/sys/asan.h
+++ b/sys/sys/asan.h
@@ -57,10 +57,12 @@
 void kasan_init_early(vm_offset_t, size_t);
 void kasan_shadow_map(vm_offset_t, size_t);
 void kasan_mark(const void *, size_t, size_t, uint8_t);
+void kasan_kstack_unpoison(struct thread *);
 #else /* KASAN */
 #define kasan_init()
 #define kasan_shadow_map(a, s)
 #define kasan_mark(p, s, l, c)
+#define kasan_kstack_unpoison(t)
 #endif /* !KASAN */
 
 #endif /* !_SYS_ASAN_H_ */