diff --git a/libc-test/build.rs b/libc-test/build.rs
index 27ead960def1c..dab9978a038d6 100644
--- a/libc-test/build.rs
+++ b/libc-test/build.rs
@@ -2444,7 +2444,8 @@ fn test_emscripten(target: &str) {
 
     let mut cfg = ctest_cfg();
     cfg.define("_GNU_SOURCE", None); // FIXME: ??
-    cfg.flag("-pthread"); // Enable POSIX threads support.
+    cfg.flag("-pthread");
+    cfg.flag("--shared-memory");
 
     headers! { cfg:
                "aio.h",