diff --git a/history.md b/history.md
index 4f79715b..5b75d77b 100644
--- a/history.md
+++ b/history.md
@@ -4,6 +4,7 @@
 - Change default Accept header to `*/*`
 - Use a more descriptive User-Agent header by default
 - Drop RC4-MD5 from default cipher list (will have no affect on most users)
+- Only prepend http:// to URIs without a scheme
 
 # 1.7.2
 
diff --git a/lib/restclient/request.rb b/lib/restclient/request.rb
index 024e3fdb..09334d51 100644
--- a/lib/restclient/request.rb
+++ b/lib/restclient/request.rb
@@ -270,8 +270,22 @@ def net_http_do_request(http, req, body=nil, &block)
       end
     end
 
+    # Parse a string into a URI object. If the string has no HTTP-like scheme
+    # (i.e. scheme followed by '//'), a scheme of 'http' will be added. This
+    # mimics the behavior of browsers and user agents like cURL.
+    #
+    # @param url [String] A URL string.
+    #
+    # @return [URI]
+    #
+    # @raise URI::InvalidURIError on invalid URIs
+    #
     def parse_url(url)
-      url = "http://#{url}" unless url.match(/^http/)
+      # Prepend http:// unless the string already contains an RFC 3986 scheme
+      # followed by two forward slashes. (The slashes are not part of the URI
+      # RFC, but specified by the URL RFC 1738.)
+      # https://tools.ietf.org/html/rfc3986#section-3.1
+      url = 'http://' + url unless url.match(/\A[a-z][a-z0-9+.-]*:\/\//i)
       URI.parse(url)
     end
 
diff --git a/spec/unit/request_spec.rb b/spec/unit/request_spec.rb
index d69cf542..5fc92a69 100644
--- a/spec/unit/request_spec.rb
+++ b/spec/unit/request_spec.rb
@@ -68,14 +68,36 @@
     end
   end
 
-  it "parses a url into a URI object" do
-    URI.should_receive(:parse).with('http://example.com/resource')
-    @request.parse_url('http://example.com/resource')
-  end
+  describe '.parse_url' do
+    it "parses a url into a URI object" do
+      URI.should_receive(:parse).with('http://example.com/resource')
+      @request.parse_url('http://example.com/resource')
+    end
+
+    it "adds http:// to the front of resources specified in the syntax example.com/resource" do
+      URI.should_receive(:parse).with('http://example.com/resource')
+      @request.parse_url('example.com/resource')
+    end
+
+    it 'adds http:// to resources containing a colon' do
+      URI.should_receive(:parse).with('http://example.com:1234')
+      @request.parse_url('example.com:1234')
+    end
 
-  it "adds http:// to the front of resources specified in the syntax example.com/resource" do
-    URI.should_receive(:parse).with('http://example.com/resource')
-    @request.parse_url('example.com/resource')
+    it 'does not add http:// to the front of https resources' do
+      URI.should_receive(:parse).with('https://example.com/resource')
+      @request.parse_url('https://example.com/resource')
+    end
+
+    it 'does not add http:// to the front of capital HTTP resources' do
+      URI.should_receive(:parse).with('HTTP://example.com/resource')
+      @request.parse_url('HTTP://example.com/resource')
+    end
+
+    it 'does not add http:// to the front of capital HTTPS resources' do
+      URI.should_receive(:parse).with('HTTPS://example.com/resource')
+      @request.parse_url('HTTPS://example.com/resource')
+    end
   end
 
   describe "user - password" do