diff --git a/swiftclient/client.py b/swiftclient/client.py
index 544247a..e81d2c6 100644
--- a/swiftclient/client.py
+++ b/swiftclient/client.py
@@ -24,6 +24,8 @@ import warnings
 
 from distutils.version import StrictVersion
 from requests.exceptions import RequestException, SSLError
+from requests.utils import check_header_validity
+from requests._internal_utils import to_native_string
 from six.moves import http_client
 from six.moves.urllib.parse import quote as _quote, unquote
 from six.moves.urllib.parse import urljoin, urlparse, urlunparse
@@ -86,10 +88,17 @@ if StrictVersion(requests.__version__) < StrictVersion('2.0.0') \
     from requests.structures import CaseInsensitiveDict
 
     def prepare_unicode_headers(self, headers):
+        """Prepares the given HTTP headers."""
+        self.headers = CaseInsensitiveDict()
         if headers:
-            self.headers = CaseInsensitiveDict(headers)
-        else:
-            self.headers = CaseInsensitiveDict()
+            for header in headers.items():
+                # Raise exception on invalid header value.
+                check_header_validity(header)
+                name, value = header
+                try:
+                    self.headers[to_native_string(name)] = value
+                except UnicodeDecodeError:
+                    self.headers[name] = value
     requests.models.PreparedRequest.prepare_headers = prepare_unicode_headers
 
 logger = logging.getLogger("swiftclient")