diff --git a/libcxx/include/__debug b/libcxx/include/__debug
--- a/libcxx/include/__debug
+++ b/libcxx/include/__debug
@@ -12,7 +12,6 @@
 
 #include <__assert>
 #include <__config>
-#include <iosfwd>
 #include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
diff --git a/libcxx/include/experimental/iterator b/libcxx/include/experimental/iterator
--- a/libcxx/include/experimental/iterator
+++ b/libcxx/include/experimental/iterator
@@ -57,6 +57,7 @@
 #include <__utility/forward.h>
 #include <__utility/move.h>
 #include <experimental/__config>
+#include <iosfwd> // char_traits
 #include <iterator>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
diff --git a/libcxx/include/module.modulemap b/libcxx/include/module.modulemap
--- a/libcxx/include/module.modulemap
+++ b/libcxx/include/module.modulemap
@@ -648,7 +648,10 @@
       module move_iterator         { private header "__iterator/move_iterator.h" }
       module next                  { private header "__iterator/next.h" }
       module ostream_iterator      { private header "__iterator/ostream_iterator.h" }
-      module ostreambuf_iterator   { private header "__iterator/ostreambuf_iterator.h" }
+      module ostreambuf_iterator   {
+        private header "__iterator/ostreambuf_iterator.h"
+        export iosfwd
+      }
       module permutable            { private header "__iterator/permutable.h" }
       module prev                  { private header "__iterator/prev.h" }
       module projected             { private header "__iterator/projected.h" }