diff --git a/lib/string.in.h b/lib/string.in.h
index ba7ca53..32ff5de 100644
--- a/lib/string.in.h
+++ b/lib/string.in.h
@@ -18,6 +18,8 @@
 
 #ifndef _GL_STRING_H
 
+#include <config.h>
+
 /* The include_next requires a split double-inclusion guard.  */
 address@hidden@ @NEXT_STRING_H@