diff --git a/bsd/sys/cddl/compat/opensolaris/sys/param.h b/bsd/sys/cddl/compat/opensolaris/sys/param.h
index 19f158a6cdaab420c5712613619902697c487368..a6e3574dd8205645c21b2a80a1ca40e0a056377d 100644
--- a/bsd/sys/cddl/compat/opensolaris/sys/param.h
+++ b/bsd/sys/cddl/compat/opensolaris/sys/param.h
@@ -35,7 +35,7 @@
 #define	PAGESIZE	PAGE_SIZE
 
 #ifdef _KERNEL
-#define	ptob(x)		((uint64_t)(x) << PAGE_SHIFT)
+#define	ptob(x)		((uint64_t)(x) * PAGE_SIZE)
 #endif
 
 #endif