--- /n/sources/plan9/sys/include/libc.h	Wed Sep 18 22:45:28 2013
+++ /sys/include/libc.h	Sun Jun 28 00:00:00 2026
@@ -9,7 +9,7 @@
  * mem routines
  */
 extern	void*	memccpy(void*, void*, int, ulong);
-extern	void*	memset(void*, int, ulong);
+extern	void*	memset(void*, int, uintptr);
 extern	int	memcmp(void*, void*, ulong);
 extern	void*	memcpy(void*, void*, ulong);
 extern	void*	memmove(void*, void*, ulong);
--- /n/sources/plan9/sys/src/libc/port/memset.c	Sat Jan 10 10:00:05 2015
+++ /sys/src/libc/port/memset.c	Sun Jun 28 00:00:00 2026
@@ -2,7 +2,7 @@
 #include	<libc.h>
 
 void*
-memset(void *ap, int c, ulong n)
+memset(void *ap, int c, uintptr n)
 {
 	char *p;
 
--- /n/sources/plan9/sys/man/2/memory	Sat Jun 14 00:00:00 2025
+++ /sys/man/2/memory	Sun Jun 28 00:00:00 2026
@@ -26,7 +26,7 @@
 void*	memmove(void *s1, void *s2, ulong n)
 .PP
 .B
-void*	memset(void *s, int c, ulong n)
+void*	memset(void *s, int c, uintptr n)
 .SH DESCRIPTION
 These functions operate efficiently on memory areas
 (arrays of bytes bounded by a count, not terminated by a zero byte).
@@ -128,6 +128,23 @@
 .I memmove
 are handed a negative count, they abort.
 .PP
+The last argument to
+.I memset
+is traditionally
+.IR ulong ,
+but that isn't adequate on 64-bit systems.
+.PP
+All the
+.I ulong
+.I n
+arguments should be
+.I uintptr
+instead;
+.I memset
+is the critical one for zeroing
+.I malloc
+results.
+.PP
 .I Tsmemcmp
 is a variant of
 .I memcmp