1 files changed, 8 insertions, 2 deletions
diff --git a/mrbgems/mruby-io/mrblib/io.rb b/mrbgems/mruby-io/mrblib/io.rb
index 32bac1f0d..6b83644ef 100644
--- a/mrbgems/mruby-io/mrblib/io.rb
+++ b/mrbgems/mruby-io/mrblib/io.rb
@@ -170,8 +170,14 @@ class IO
   end
 
   def _read_buf
-    return @buf if @buf && @buf.bytesize > 0
-    @buf = sysread(BUF_SIZE)
+    return @buf if @buf && @buf.bytesize >= 4 # maximum UTF-8 character is 4 bytes
+    @buf ||= ""
+    begin
+      @buf += sysread(BUF_SIZE)
+    rescue EOFError => e
+      raise e if @buf.empty?
+    end
+    @buf
   end
 
   def ungetc(substr)