diff --git a/headers/posix/stdio.h b/headers/posix/stdio.h
index 7f876f27cb..59364e8b03 100644
--- a/headers/posix/stdio.h
+++ b/headers/posix/stdio.h
@@ -101,6 +101,10 @@ extern FILE		*open_memstream(char **buf, size_t *size);
 
 /* callback streams */
 #ifdef _GNU_SOURCE
+typedef ssize_t (*cookie_read_function_t)(void *cookie, char *buf, size_t size);
+typedef ssize_t (*cookie_write_function_t)(void *cookie, const char *buf, size_t size);
+typedef ssize_t (*cookie_seek_function_t)(void *cookie, off_t *offset, int whence);
+typedef ssize_t (*cookie_close_function_t)(void *cookie);
 typedef struct {
 	cookie_read_function_t  *read;
 	cookie_write_function_t *write;