diff --git a/sys/include/bio.h b/sys/include/bio.h
index 4782932e3..f358c962c 100644
--- a/sys/include/bio.h
+++ b/sys/include/bio.h
@@ -32,6 +32,7 @@ struct	Biobufhdr
 	uchar*	bbuf;		/* pointer to beginning of buffer */
 	uchar*	ebuf;		/* pointer to end of buffer */
 	uchar*	gbuf;		/* pointer to good data in buf */
+	void	(*errorf)(char *);	/* called on error if not nil */
 };
 
 struct	Biobuf
@@ -70,5 +71,7 @@ int	Bterm(Biobufhdr*);
 int	Bungetc(Biobufhdr*);
 int	Bungetrune(Biobufhdr*);
 long	Bwrite(Biobufhdr*, void*, long);
+void	Blethal(Biobufhdr*, void(*)(char*));
+void	Berror(Biobufhdr*, char*, ...);
 
 #pragma	varargck	argpos	Bprint	2
diff --git a/sys/src/cmd/8c/swt.c b/sys/src/cmd/8c/swt.c
index 46fd71eb4..d2c48b40a 100644
--- a/sys/src/cmd/8c/swt.c
+++ b/sys/src/cmd/8c/swt.c
@@ -199,6 +199,7 @@ outcode(void)
 		return;
 	}
 	Binit(&b, f, OWRITE);
+	Blethal(&b, nil);
 	Bseek(&b, 0L, 2);
 	outhist(&b);
 	for(sym=0; sym<NSYM; sym++) {
diff --git a/sys/src/libbio/bflush.c b/sys/src/libbio/bflush.c
index d4339eea7..44b0d59a9 100644
--- a/sys/src/libbio/bflush.c
+++ b/sys/src/libbio/bflush.c
@@ -20,6 +20,7 @@ Bflush(Biobufhdr *bp)
 		}
 		bp->state = Binactive;
 		bp->ocount = 0;
+		Berror(bp, "write error: %r");
 		break;
 
 	case Bracteof:
diff --git a/sys/src/libbio/bgetc.c b/sys/src/libbio/bgetc.c
index 1119c4517..0cabc0716 100644
--- a/sys/src/libbio/bgetc.c
+++ b/sys/src/libbio/bgetc.c
@@ -28,8 +28,10 @@ loop:
 	bp->gbuf = bp->bbuf;
 	if(i <= 0) {
 		bp->state = Bracteof;
-		if(i < 0)
+		if(i < 0) {
 			bp->state = Binactive;
+			Berror(bp, "read error: %r");
+		}
 		return Beof;
 	}
 	if(i < bp->bsize) {
diff --git a/sys/src/libbio/binit.c b/sys/src/libbio/binit.c
index 75cee333b..ef705e667 100644
--- a/sys/src/libbio/binit.c
+++ b/sys/src/libbio/binit.c
@@ -83,6 +83,7 @@ Binits(Biobufhdr *bp, int f, int mode, uchar *p, int size)
 	bp->rdline = 0;
 	bp->offset = 0;
 	bp->runesize = 0;
+	bp->errorf = nil;
 	return 0;
 }
 
diff --git a/sys/src/libbio/brdline.c b/sys/src/libbio/brdline.c
index c116e3859..4168d1e10 100644
--- a/sys/src/libbio/brdline.c
+++ b/sys/src/libbio/brdline.c
@@ -47,6 +47,8 @@ Brdline(Biobufhdr *bp, int delim)
 	ip = (char*)bp->bbuf + i;
 	while(i < bp->bsize) {
 		j = read(bp->fid, ip, bp->bsize-i);
+		if(j < 0)
+			Berror(bp, "read error: %r");
 		if(j <= 0) {
 			/*
 			 * end of file with no delim
diff --git a/sys/src/libbio/brdstr.c b/sys/src/libbio/brdstr.c
index b5727ad2a..a1b14f885 100644
--- a/sys/src/libbio/brdstr.c
+++ b/sys/src/libbio/brdstr.c
@@ -67,6 +67,8 @@ Brdstr(Biobufhdr *bp, int delim, int nulldelim)
 		ip = (char*)bp->bbuf + i;
 		while(i < bp->bsize) {
 			j = read(bp->fid, ip, bp->bsize-i);
+			if(j < 0)
+				Berror(bp, "read error: %r");
 			if(j <= 0 && i == 0)
 				return p;
 			if(j <= 0 && i > 0){
diff --git a/sys/src/libbio/bread.c b/sys/src/libbio/bread.c
index 9780ffac1..8e57d8e07 100644
--- a/sys/src/libbio/bread.c
+++ b/sys/src/libbio/bread.c
@@ -23,8 +23,10 @@ Bread(Biobufhdr *bp, void *ap, long count)
 			i = read(bp->fid, bp->bbuf, bp->bsize);
 			if(i <= 0) {
 				bp->state = Bracteof;
-				if(i < 0)
+				if(i < 0) {
+					Berror(bp, "read error: %r");
 					bp->state = Binactive;
+				}
 				break;
 			}
 			bp->gbuf = bp->bbuf;
diff --git a/sys/src/libbio/bwrite.c b/sys/src/libbio/bwrite.c
index ae7a7d97c..03f46779b 100644
--- a/sys/src/libbio/bwrite.c
+++ b/sys/src/libbio/bwrite.c
@@ -24,8 +24,10 @@ Bwrite(Biobufhdr *bp, void *ap, long count)
 			i = write(bp->fid, bp->bbuf, bp->bsize);
 			if(i != bp->bsize) {
 				errstr(errbuf, sizeof errbuf);
-				if(strstr(errbuf, "interrupt") == nil)
+				if(strstr(errbuf, "interrupt") == nil) {
 					bp->state = Binactive;
+					Berror(bp, "write error: %s", errbuf);
+				}
 				errstr(errbuf, sizeof errbuf);
 				return Beof;
 			}
diff --git a/sys/src/libbio/mkfile b/sys/src/libbio/mkfile
index a8c21dbaa..3b40fd25c 100644
--- a/sys/src/libbio/mkfile
+++ b/sys/src/libbio/mkfile
@@ -9,6 +9,7 @@ OFILES=\
 	bgetc.$O\
 	bgetd.$O\
 	binit.$O\
+	blethal.$O\
 	boffset.$O\
 	bprint.$O\
 	bputrune.$O\