diff --git a/moto/s3/utils.py b/moto/s3/utils.py
index 7dd0accc..19b0cfdf 100644
--- a/moto/s3/utils.py
+++ b/moto/s3/utils.py
@@ -8,8 +8,8 @@ bucket_name_regex = re.compile("(.+).s3.amazonaws.com")
 def bucket_name_from_url(url):
     domain = urlparse.urlparse(url).netloc
 
-    # If 'www' prefixed, strip it.
-    domain = domain.replace("www.", "")
+    if domain.startswith('www.'):
+        domain = domain[4:]
 
     if 'amazonaws.com' in domain:
         bucket_result = bucket_name_regex.search(domain)
diff --git a/tests/test_s3/test_s3_utils.py b/tests/test_s3/test_s3_utils.py
index 5b03d61f..cb8bd8b8 100644
--- a/tests/test_s3/test_s3_utils.py
+++ b/tests/test_s3/test_s3_utils.py
@@ -7,7 +7,7 @@ def test_base_url():
 
 
 def test_localhost_bucket():
-    expect(bucket_name_from_url('https://foobar.localhost:5000/abc')).should.equal("foobar")
+    expect(bucket_name_from_url('https://wfoobar.localhost:5000/abc')).should.equal("wfoobar")
 
 
 def test_localhost_without_bucket():