--- a/src/header/stdio/ext.rs
+++ b/src/header/stdio/ext.rs
@@ -1,8 +1,15 @@
 use crate::{
-    header::stdio::{F_NORD, F_NOWR, FILE},
+    header::stdio::{F_ERR, F_NORD, F_NOWR, FILE},
     platform::types::{c_int, size_t},
 };
 
+#[unsafe(no_mangle)]
+pub extern "C" fn __freadahead(stream: *mut FILE) -> size_t {
+    let stream = unsafe { &mut *stream }.lock();
+
+    (stream.read_size.saturating_sub(stream.read_pos) + stream.unget.len()) as size_t
+}
+
 #[unsafe(no_mangle)]
 pub extern "C" fn __fpending(stream: *mut FILE) -> size_t {
     let stream = unsafe { &mut *stream }.lock();
@@ -24,6 +31,13 @@ pub extern "C" fn __fwritable(stream: *mut FILE) -> c_int {
     c_int::from(stream.flags & F_NOWR == 0)
 }
 
+#[unsafe(no_mangle)]
+pub extern "C" fn __fseterr(stream: *mut FILE) {
+    let mut stream = unsafe { &mut *stream }.lock();
+
+    stream.flags |= F_ERR;
+}
+
 //TODO: Check last operation when read-write
 #[unsafe(no_mangle)]
 pub extern "C" fn __freading(stream: *mut FILE) -> c_int {
--- a/include/stdio_ext.h
+++ b/include/stdio_ext.h
@@ -2,5 +2,21 @@
 #define _STDIO_EXT_H
 
 #include <stdio.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+size_t __freadahead(FILE *stream);
+size_t __fpending(FILE *stream);
+int __freadable(FILE *stream);
+int __freading(FILE *stream);
+void __fseterr(FILE *stream);
+int __fwritable(FILE *stream);
+int __fwriting(FILE *stream);
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
 
 #endif /* _STDIO_EXT_H */