diff --git a/test/lib/minitest/unit.rb b/test/lib/minitest/unit.rb
index 62f89e97e5..aa53ef06f6 100644
--- a/test/lib/minitest/unit.rb
+++ b/test/lib/minitest/unit.rb
@@ -998,7 +998,7 @@ module MiniTest
           else
             @errors += 1
             bt = MiniTest::filter_backtrace(e.backtrace).join "\n    "
-            "Error:\n#{klass}##{meth}:\n#{e.class}: #{e.message}\n    #{bt}\n"
+            "Error:\n#{klass}##{meth}:\n#{e.class}: #{e.message.b}\n    #{bt}\n"
           end
       @report << e
       e[0, 1]
diff --git a/test/lib/test/unit/assertions.rb b/test/lib/test/unit/assertions.rb
index cdd188478f..41463ea61b 100644
--- a/test/lib/test/unit/assertions.rb
+++ b/test/lib/test/unit/assertions.rb
@@ -801,7 +801,7 @@ eom
           total = @count.to_s
           fmt = "%#{total.size}d"
           @failures.map {|k, (n, v)|
-            "\n#{i+=1}. [#{fmt%n}/#{total}] Assertion for #{k.inspect}\n#{v.message.gsub(/^/, '   | ')}"
+            "\n#{i+=1}. [#{fmt%n}/#{total}] Assertion for #{k.inspect}\n#{v.message.b.gsub(/^/, '   | ')}"
           }.join("\n")
         end