diff --git a/include/boost/iostreams/filter/bzip2.hpp b/include/boost/iostreams/filter/bzip2.hpp
index e769ba1..e55dbb2 100755
--- a/include/boost/iostreams/filter/bzip2.hpp
+++ b/include/boost/iostreams/filter/bzip2.hpp
@@ -225,7 +225,7 @@ private:
     typedef symmetric_filter_adapter<impl_type, Alloc>  base_type;
 public:
     typedef typename base_type::char_type               char_type;
-    typedef typename base_type::category                io_category;
+    typedef typename base_type::io_category             io_category;
     basic_bzip2_compressor( const bzip2_params& = bzip2::default_block_size, 
                             std::streamsize buffer_size = 
                                 default_buffer_size );
@@ -249,7 +249,7 @@ private:
     typedef symmetric_filter_adapter<impl_type, Alloc>  base_type;
 public:
     typedef typename base_type::char_type               char_type;
-    typedef typename base_type::category                io_category;
+    typedef typename base_type::io_category             io_category;
     basic_bzip2_decompressor( bool small = bzip2::default_small,
                               std::streamsize buffer_size = 
                                   default_buffer_size );
diff --git a/include/boost/iostreams/filter/zlib.hpp b/include/boost/iostreams/filter/zlib.hpp
index 63052d6..8066eed 100755
--- a/include/boost/iostreams/filter/zlib.hpp
+++ b/include/boost/iostreams/filter/zlib.hpp
@@ -237,7 +237,7 @@ private:
     typedef symmetric_filter_adapter<impl_type, Alloc>  base_type;
 public:
     typedef typename base_type::char_type               char_type;
-    typedef typename base_type::category                io_category;
+    typedef typename base_type::io_category             io_category;
     basic_zlib_compressor( const zlib_params& = zlib::default_compression, 
                            std::streamsize buffer_size = default_buffer_size );
                            // Note: use large buffer.
@@ -262,7 +262,7 @@ private:
     typedef symmetric_filter_adapter<impl_type, Alloc>  base_type;
 public:
     typedef typename base_type::char_type               char_type;
-    typedef typename base_type::category                io_category;
+    typedef typename base_type::io_category             io_category;
     basic_zlib_decompressor( int window_bits = zlib::default_window_bits,
                              std::streamsize buffer_size = 
                                  default_buffer_size );