--- /sys/src/9k/port/segment.c
+++ /sys/src/9k/port/segment.c
@@ -270,8 +270,7 @@ isoverlap(Proc* p, uintptr va, usize len)
 		ns = p->seg[i];
 		if(ns == 0)
 			continue;
-		if((newtop > ns->base && newtop <= ns->top) ||
-		   (va >= ns->base && va < ns->top))
+		if(newtop > ns->base && va < ns->top)
 			return ns;
 	}
 	return nil;
--- /sys/src/9k/port/sysseg.c
+++ /sys/src/9k/port/sysseg.c
@@ -108,7 +108,7 @@ ibrk(uintptr addr, int seg)
 		ns = up->seg[i];
 		if(ns == 0 || ns == s)
 			continue;
-		if(newtop >= ns->base && newtop < ns->top)
+		if(newtop > ns->base && s->base < ns->top)
 			error(Esoverlap);
 	}