diff --git a/lib/tokenize.h b/lib/tokenize.h
index 848edf31f..f7dad0fe1 100644
--- a/lib/tokenize.h
+++ b/lib/tokenize.h
@@ -27,6 +27,7 @@
 #include <list>
 #include <vector>
 #include <set>
+#include <iosfwd>
 
 class Token;
 class ErrorLogger;