diff --git a/sys/src/ape/lib/ap/stdio/_IO_newfile.c b/sys/src/ape/lib/ap/stdio/_IO_newfile.c
index 6a016ec5d..f559fdf8c 100644
--- a/sys/src/ape/lib/ap/stdio/_IO_newfile.c
+++ b/sys/src/ape/lib/ap/stdio/_IO_newfile.c
@@ -5,6 +5,7 @@
 
 #define _PLAN9_SOURCE
 #include <lock.h>
+#include <errno.h>
 
 FILE *_IO_newfile(void)
 {
@@ -21,7 +22,9 @@ FILE *_IO_newfile(void)
 	}
 	f = fx;
 	unlock(&fl);
-	if(f->state!=CLOSED)
+	if(f->state!=CLOSED){
+		errno = EMFILE;
 		return NULL;
+	}
 	return f;
 }
diff --git a/sys/src/ape/lib/ap/stdio/fdopen.c b/sys/src/ape/lib/ap/stdio/fdopen.c
index cb10d98e7..b3061fbe7 100644
--- a/sys/src/ape/lib/ap/stdio/fdopen.c
+++ b/sys/src/ape/lib/ap/stdio/fdopen.c
@@ -2,6 +2,7 @@
  * Posix stdio -- fdopen
  */
 #include "iolib.h"
+#include <errno.h>
 /*
  * Open the named file with the given mode, using the given FILE
  * Legal modes are given below, `additional characters may follow these sequences':
@@ -15,12 +16,15 @@
 FILE *fdopen(const int fd, const char *mode){
 	FILE *f;
 
+	if(fd < 0){
+		errno = EBADF;
+		return NULL;
+	}
 	if((f = _IO_newfile()) == NULL)
 		return NULL;
 	f->fd=fd;
 	if(mode[0]=='a')
 		lseek(f->fd, 0L, 2);
-	if(f->fd==-1) return NULL;
 	f->flags=0;
 	f->state=OPEN;
 	f->buf=0;