diff --git a/src/unix/notbsd/linux/mod.rs b/src/unix/notbsd/linux/mod.rs
index e48be8bc968503471915ebcc2f528e1ec3f4554d..62e2262113e220a85cf296934a812cd424ac7b7b 100644
--- a/src/unix/notbsd/linux/mod.rs
+++ b/src/unix/notbsd/linux/mod.rs
@@ -316,6 +316,8 @@ extern {
                      offset: ::off_t, len: ::off_t) -> ::c_int;
     pub fn posix_fallocate(fd: ::c_int, offset: ::off_t,
                            len: ::off_t) -> ::c_int;
+    pub fn readahead(fd: ::c_int, offset: ::off64_t,
+                     count: ::size_t) -> ::ssize_t;
 }
 
 cfg_if! {