diff --git a/src/unix/bsd/freebsdlike/dragonfly/mod.rs b/src/unix/bsd/freebsdlike/dragonfly/mod.rs
index 3ec1cc3a79e90..014636312d3a6 100644
--- a/src/unix/bsd/freebsdlike/dragonfly/mod.rs
+++ b/src/unix/bsd/freebsdlike/dragonfly/mod.rs
@@ -1086,6 +1086,12 @@ extern "C" {
     pub fn statfs(path: *const ::c_char, buf: *mut statfs) -> ::c_int;
     pub fn fstatfs(fd: ::c_int, buf: *mut statfs) -> ::c_int;
     pub fn uname(buf: *mut ::utsname) -> ::c_int;
+    pub fn memmem(
+        haystack: *const ::c_void,
+        haystacklen: ::size_t,
+        needle: *const ::c_void,
+        needlelen: ::size_t,
+    ) -> *mut ::c_void;
 }
 
 cfg_if! {
diff --git a/src/unix/bsd/freebsdlike/freebsd/mod.rs b/src/unix/bsd/freebsdlike/freebsd/mod.rs
index 15bfc1abec3bd..1b714b77514ab 100644
--- a/src/unix/bsd/freebsdlike/freebsd/mod.rs
+++ b/src/unix/bsd/freebsdlike/freebsd/mod.rs
@@ -1435,6 +1435,12 @@ extern "C" {
         flags: ::c_int,
         timeout: *const ::timespec,
     ) -> ::ssize_t;
+    pub fn memmem(
+        haystack: *const ::c_void,
+        haystacklen: ::size_t,
+        needle: *const ::c_void,
+        needlelen: ::size_t,
+    ) -> *mut ::c_void;
 }
 
 #[link(name = "util")]
diff --git a/src/unix/bsd/netbsdlike/netbsd/mod.rs b/src/unix/bsd/netbsdlike/netbsd/mod.rs
index 2686ab92c1488..48c9038631b1d 100644
--- a/src/unix/bsd/netbsdlike/netbsd/mod.rs
+++ b/src/unix/bsd/netbsdlike/netbsd/mod.rs
@@ -1894,6 +1894,12 @@ extern "C" {
     ) -> ::c_int;
 
     pub fn _lwp_self() -> lwpid_t;
+    pub fn memmem(
+        haystack: *const ::c_void,
+        haystacklen: ::size_t,
+        needle: *const ::c_void,
+        needlelen: ::size_t,
+    ) -> *mut ::c_void;
 }
 
 #[link(name = "util")]
diff --git a/src/unix/bsd/netbsdlike/openbsd/mod.rs b/src/unix/bsd/netbsdlike/openbsd/mod.rs
index f3e7279f6d8ec..8e1bfcb578eb1 100644
--- a/src/unix/bsd/netbsdlike/openbsd/mod.rs
+++ b/src/unix/bsd/netbsdlike/openbsd/mod.rs
@@ -1478,6 +1478,12 @@ extern "C" {
         addr: caddr_t,
         data: ::c_int,
     ) -> ::c_int;
+    pub fn memmem(
+        haystack: *const ::c_void,
+        haystacklen: ::size_t,
+        needle: *const ::c_void,
+        needlelen: ::size_t,
+    ) -> *mut ::c_void;
 }
 
 cfg_if! {
diff --git a/src/unix/linux_like/linux/gnu/mod.rs b/src/unix/linux_like/linux/gnu/mod.rs
index 80a1c4eab5157..ad5b310bb18ca 100644
--- a/src/unix/linux_like/linux/gnu/mod.rs
+++ b/src/unix/linux_like/linux/gnu/mod.rs
@@ -959,6 +959,12 @@ extern "C" {
         buflen: ::size_t,
         flags: ::c_uint,
     ) -> ::ssize_t;
+    pub fn memmem(
+        haystack: *const ::c_void,
+        haystacklen: ::size_t,
+        needle: *const ::c_void,
+        needlelen: ::size_t,
+    ) -> *mut ::c_void;
 }
 
 #[link(name = "util")]
diff --git a/src/unix/linux_like/linux/musl/mod.rs b/src/unix/linux_like/linux/musl/mod.rs
index 2c5d375a1aa59..0bddd64abae18 100644
--- a/src/unix/linux_like/linux/musl/mod.rs
+++ b/src/unix/linux_like/linux/musl/mod.rs
@@ -416,6 +416,12 @@ extern "C" {
         cpuset: *const ::cpu_set_t,
     ) -> ::c_int;
     pub fn sched_getcpu() -> ::c_int;
+    pub fn memmem(
+        haystack: *const ::c_void,
+        haystacklen: ::size_t,
+        needle: *const ::c_void,
+        needlelen: ::size_t,
+    ) -> *mut ::c_void;
 }
 
 cfg_if! {