diff --git a/libc-test/build.rs b/libc-test/build.rs
index 28ac5a51b97b4..2f59a442af184 100644
--- a/libc-test/build.rs
+++ b/libc-test/build.rs
@@ -77,6 +77,7 @@ fn main() {
         cfg.header("netinet/in.h");
         cfg.header("netinet/ip.h");
         cfg.header("netinet/tcp.h");
+        cfg.header("resolv.h");
         cfg.header("pthread.h");
         cfg.header("dlfcn.h");
         cfg.header("signal.h");
@@ -468,6 +469,16 @@ fn main() {
             // it's in a header file?
             "endpwent" if android => true,
 
+            // Apparently res_init exists on Android, but isn't defined in a header:
+            // https://mail.gnome.org/archives/commits-list/2013-May/msg01329.html
+            "res_init" if android => true,
+
+            // On macOS and iOS, res_init is available, but requires linking with libresolv:
+            // http://blog.achernya.com/2013/03/os-x-has-silly-libsystem.html
+            // See discussion for skipping here:
+            // https://github.com/rust-lang/libc/pull/585#discussion_r114561460
+            "res_init" if apple => true,
+
             _ => false,
         }
     });
diff --git a/src/unix/mod.rs b/src/unix/mod.rs
index 7ebf0d9e0bac5..a235d6a422017 100644
--- a/src/unix/mod.rs
+++ b/src/unix/mod.rs
@@ -694,6 +694,14 @@ extern {
                        res: *mut *mut addrinfo) -> ::c_int;
     pub fn freeaddrinfo(res: *mut addrinfo);
     pub fn gai_strerror(errcode: ::c_int) -> *const ::c_char;
+    #[cfg_attr(any(
+                   all(target_os = "linux", not(target_env = "musl")),
+                   target_os = "freebsd",
+                   target_os = "dragonfly"),
+               link_name = "__res_init")]
+    #[cfg_attr(any(target_os = "macos", target_os = "ios"),
+               link_name = "res_9_init")]
+    pub fn res_init() -> ::c_int;
 
     #[cfg_attr(target_os = "netbsd", link_name = "__gmtime_r50")]
     pub fn gmtime_r(time_p: *const time_t, result: *mut tm) -> *mut tm;