diff --git a/lib/libc/stdlib/merge.c b/lib/libc/stdlib/merge.c
--- a/lib/libc/stdlib/merge.c
+++ b/lib/libc/stdlib/merge.c
@@ -52,7 +52,7 @@
  * (The default is pairwise merging.)
  */
 
-#include <sys/types.h>
+#include <sys/param.h>
 
 #include <errno.h>
 #include <stdlib.h>
@@ -97,9 +97,7 @@
  * boundaries.
  */
 /* Assumption: PSIZE is a power of 2. */
-#define EVAL(p) (u_char **)						\
-	((u_char *)0 +							\
-	    (((u_char *)p + PSIZE - 1 - (u_char *) 0) & ~(PSIZE - 1)))
+#define EVAL(p) (u_char **)roundup2((uintptr_t)p, PSIZE)
 
 #ifdef I_AM_MERGESORT_B
 int mergesort_b(void *, size_t, size_t, cmp_t);