diff --git a/libgit2-sys/build.rs b/libgit2-sys/build.rs
index e89a9a0ad2..25a16a3885 100644
--- a/libgit2-sys/build.rs
+++ b/libgit2-sys/build.rs
@@ -93,7 +93,7 @@ fn main() {
         add_c_files(&mut cfg, "libgit2/src/unix");
         cfg.flag("-fvisibility=hidden");
     }
-    if target.contains("solaris") {
+    if target.contains("solaris") || target.contains("illumos") {
         cfg.define("_POSIX_C_SOURCE", "200112L");
         cfg.define("__EXTENSIONS__", None);
     }