diff --git a/sys/src/9/pc/dat.h b/sys/src/9/pc/dat.h
index 3941a925e..278f70893 100644
--- a/sys/src/9/pc/dat.h
+++ b/sys/src/9/pc/dat.h
@@ -343,7 +343,7 @@ enum {
 
 struct ISAConf {
 	char	*type;
-	ulong	port;
+	uvlong	port;
 	int	irq;
 	ulong	dma;
 	ulong	mem;
diff --git a/sys/src/9/pc/devarch.c b/sys/src/9/pc/devarch.c
index d637d5aa3..5ba04b59c 100644
--- a/sys/src/9/pc/devarch.c
+++ b/sys/src/9/pc/devarch.c
@@ -1247,7 +1247,7 @@ isaconfig(char *class, int ctlrno, ISAConf *isa)
 		if(cistrncmp(p, "type=", 5) == 0)
 			isa->type = p + 5;
 		else if(cistrncmp(p, "port=", 5) == 0)
-			isa->port = strtoul(p+5, &p, 0);
+			isa->port = strtoull(p+5, &p, 0);
 		else if(cistrncmp(p, "irq=", 4) == 0)
 			isa->irq = strtoul(p+4, &p, 0);
 		else if(cistrncmp(p, "dma=", 4) == 0)
diff --git a/sys/src/9/pc64/dat.h b/sys/src/9/pc64/dat.h
index cc04c7c3b..6cb1cc9ed 100644
--- a/sys/src/9/pc64/dat.h
+++ b/sys/src/9/pc64/dat.h
@@ -319,7 +319,7 @@ enum {						/* MSRs */
 
 struct ISAConf {
 	char	*type;
-	ulong	port;
+	uvlong	port;
 	int	irq;
 	ulong	dma;
 	ulong	mem;