diff --git a/.travis.yml b/.travis.yml
index 970c4a7a..b1007562 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -14,7 +14,7 @@ env:
 - ARCH=i686
 
 install:
-- pip install urllib3 certifi pytz pyflakes faker nose
+- pip install urllib3 certifi pytz pyflakes faker nose future
 
 script:
 - pyflakes minio/*.py || true
diff --git a/minio/helpers.py b/minio/helpers.py
index 9151b93f..39e2f4f2 100644
--- a/minio/helpers.py
+++ b/minio/helpers.py
@@ -28,8 +28,12 @@
 # if math.ceil returns an integer and devide two integers returns a float, calculate
 # part size will cause errors, so make sure division integers returns a float.
 from __future__ import division
-import io
 
+from __future__ import unicode_literals
+# future_str is unicode or str in both Python 2 and 3
+from builtins import str as future_str
+
+import io
 import collections
 import base64
 import hashlib
@@ -654,6 +658,16 @@ def optimal_part_info(length, part_size):
 def amzprefix_user_metadata(metadata):
     m = dict()
     for k,v in metadata.items():
+       # Check if metadata value has US-ASCII encoding since it is
+       # the only one supported by HTTP headers. This will show a better
+       # exception message when users pass unsupported characters
+       # in metadata values.
+       try:
+            if isinstance(v, future_str):
+                 v.encode('us-ascii')
+       except UnicodeEncodeError:
+            raise ValueError('Metadata supports only US-ASCII characters.')
+
        if is_amz_header(k) or is_supported_header(k) or is_storageclass_header(k):
             m[k] = v
        else: