diff --git a/sys/src/libc/port/date.c b/sys/src/libc/port/date.c
index 805302432..c9526dec6 100644
--- a/sys/src/libc/port/date.c
+++ b/sys/src/libc/port/date.c
@@ -1,5 +1,6 @@
 #include <u.h>
 #include <libc.h>
+#include <ctype.h>
 
 typedef struct Tzabbrev Tzabbrev;
 typedef struct Tzoffpair Tzoffpair;
@@ -62,9 +63,6 @@ struct Tzoffpair {
 	int off;
 };
 
-#define isalpha(c)\
-	(((c)|0x60) >= 'a' && ((c)|0x60) <= 'z')
-
 /* Obsolete time zone names. Hardcoded to match RFC5322 */
 static Tzabbrev tzabbrev[] = {
 	{"UT", "GMT"}, {"GMT", "GMT"}, {"UTC", "GMT"},