diff --git a/peglib.h b/peglib.h
index 5763e7b..20b5080 100644
--- a/peglib.h
+++ b/peglib.h
@@ -41,7 +41,11 @@
 
 namespace peg {
 
+#if __clang__ == 1 && __clang_major__ == 5 && __clang_minor__ == 0 && __clang_patchlevel__ == 0
+static void* enabler = nullptr; // workaround for Clang 5.0.0
+#else
 extern void* enabler;
+#endif
 
 /*-----------------------------------------------------------------------------
  *  any