diff --git a/include/boost/regex.hpp b/include/boost/regex.hpp
index efc42fce..f4d030a9 100644
--- a/include/boost/regex.hpp
+++ b/include/boost/regex.hpp
@@ -199,7 +199,7 @@ enum syntax_element_type
 
 #ifdef BOOST_RE_DEBUG
 // dwa 09/26/00 - This is needed to suppress warnings about an ambiguous conversion
-ostream& operator<<(ostream&, syntax_element_type);
+std::ostream& operator<<(std::ostream&, syntax_element_type);
 #endif
 
 union offset_type
diff --git a/src/regex_debug.cpp b/src/regex_debug.cpp
index b6022e6f..bdbf5464 100644
--- a/src/regex_debug.cpp
+++ b/src/regex_debug.cpp
@@ -33,7 +33,7 @@
 #ifdef BOOST_RE_DEBUG
 
 namespace boost { namespace re_detail {
-ostream& operator<<(ostream& s, syntax_element_type x)
+std::ostream& operator<<(std::ostream& s, syntax_element_type x)
 {
     return s << static_cast<unsigned long>(x);
 }