diff --git a/include/boost/regex/v4/u32regex_iterator.hpp b/include/boost/regex/v4/u32regex_iterator.hpp
index ae660cec..950aa423 100644
--- a/include/boost/regex/v4/u32regex_iterator.hpp
+++ b/include/boost/regex/v4/u32regex_iterator.hpp
@@ -59,6 +59,8 @@ public:
       match_flag_type f(flags);
       if(!what.length())
          f |= regex_constants::match_not_initial_null;
+      if(base != next_start)
+         f |= regex_constants::match_not_bob;
       bool result = u32regex_search(next_start, end, what, re, f);
       if(result)
          what.set_base(base);
diff --git a/include/boost/regex/v4/u32regex_token_iterator.hpp b/include/boost/regex/v4/u32regex_token_iterator.hpp
index d9f1ee48..58d1d046 100644
--- a/include/boost/regex/v4/u32regex_token_iterator.hpp
+++ b/include/boost/regex/v4/u32regex_token_iterator.hpp
@@ -130,7 +130,7 @@ public:
          return true;
       }
       if(what.prefix().first != what[0].second)
-         flags |= match_prev_avail;
+         flags |= match_prev_avail | regex_constants::match_not_bob;
       BidirectionalIterator last_end(what[0].second);
       if(u32regex_search(last_end, end, what, re, ((what[0].first == what[0].second) ? flags | regex_constants::match_not_initial_null : flags)))
       {