diff --git a/include/boost/blank.hpp b/include/boost/blank.hpp
index 338fc68..f84f2d9 100644
--- a/include/boost/blank.hpp
+++ b/include/boost/blank.hpp
@@ -58,11 +58,31 @@ inline bool operator==(const blank&, const blank&)
     return true;
 }
 
+inline bool operator<=(const blank&, const blank&)
+{
+    return true;
+}
+
+inline bool operator>=(const blank&, const blank&)
+{
+    return true;
+}
+
+inline bool operator!=(const blank&, const blank&)
+{
+    return false;
+}
+
 inline bool operator<(const blank&, const blank&)
 {
     return false;
 }
 
+inline bool operator>(const blank&, const blank&)
+{
+    return false;
+}
+
 // streaming support
 //
 BOOST_TEMPLATED_STREAM_TEMPLATE(E,T)