diff --git a/src/unix/bsd/freebsdlike/mod.rs b/src/unix/bsd/freebsdlike/mod.rs
index 14d9f55a65c49b605aeed66f658a77ac96ac9878..376fce65fbdd30d6695cb7ca6903c564ab56814e 100644
--- a/src/unix/bsd/freebsdlike/mod.rs
+++ b/src/unix/bsd/freebsdlike/mod.rs
@@ -520,6 +520,8 @@ extern {
                         -> ::c_int;
     pub fn clock_gettime(clk_id: ::c_int, tp: *mut ::timespec) -> ::c_int;
     pub fn pthread_set_name_np(tid: ::pthread_t, name: *const ::c_char);
+    pub fn posix_fallocate(fd: ::c_int, offset: ::off_t,
+                           len: ::off_t) -> ::c_int;
 }
 
 cfg_if! {
diff --git a/src/unix/notbsd/linux/mod.rs b/src/unix/notbsd/linux/mod.rs
index 577814b66f816cf3e736bf4cf918c677f84b74e1..478f5de27493fc0249cc0e17eaad5d70e9553282 100644
--- a/src/unix/notbsd/linux/mod.rs
+++ b/src/unix/notbsd/linux/mod.rs
@@ -283,6 +283,8 @@ extern {
     pub fn ftello64(stream: *mut ::FILE) -> ::off64_t;
     pub fn fallocate(fd: ::c_int, mode: ::c_int,
                      offset: ::off_t, len: ::off_t) -> ::c_int;
+    pub fn posix_fallocate(fd: ::c_int, offset: ::off_t,
+                           len: ::off_t) -> ::c_int;
 }
 
 cfg_if! {