diff --git a/Test/objc_msgSend.m b/Test/objc_msgSend.m
index 612734d..f9b82aa 100644
--- a/Test/objc_msgSend.m
+++ b/Test/objc_msgSend.m
@@ -1,3 +1,5 @@
+// Needed with glibc to expose vasprintf
+#define _GNU_SOURCE
 #include <time.h>
 #include <stdio.h>
 #include <assert.h>