diff --git a/lib/createsend/createsend.rb b/lib/createsend/createsend.rb
index 91ff055..39be9e7 100644
--- a/lib/createsend/createsend.rb
+++ b/lib/createsend/createsend.rb
@@ -76,13 +76,17 @@ def self.authorize_url(client_id, redirect_uri, scope, state=nil)
     # Exchange a provided OAuth code for an OAuth access token, 'expires in'
     # value, and refresh token.
     def self.exchange_token(client_id, client_secret, redirect_uri, code)
-      body = "grant_type=authorization_code"
-      body << "&client_id=#{CGI.escape(client_id.to_s)}"
-      body << "&client_secret=#{CGI.escape(client_secret.to_s)}"
-      body << "&redirect_uri=#{CGI.escape(redirect_uri.to_s)}"
-      body << "&code=#{CGI.escape(code.to_s)}"
-      options = {:body => body}
-      response = HTTParty.post(@@oauth_token_uri, options)
+      response = HTTParty.post(
+        @@oauth_token_uri,
+        headers: { 'Content-Type' => 'application/x-www-form-urlencoded' },
+        body: {
+          grant_type: 'authorization_code',
+          client_id: client_id,
+          client_secret: client_secret,
+          redirect_uri: redirect_uri,
+          code: code
+        }
+      )
       if response.has_key? 'error' and response.has_key? 'error_description'
         err = "Error exchanging code for access token: "
         err << "#{response['error']} - #{response['error_description']}"
@@ -95,9 +99,14 @@ def self.exchange_token(client_id, client_secret, redirect_uri, code)
     # Refresh an OAuth access token, given an OAuth refresh token.
     # Returns a new access token, 'expires in' value, and refresh token.
     def self.refresh_access_token(refresh_token)
-      options = {
-        :body => "grant_type=refresh_token&refresh_token=#{CGI.escape(refresh_token)}" }
-      response = HTTParty.post(@@oauth_token_uri, options)
+      response = HTTParty.post(
+        @@oauth_token_uri,
+        headers: { 'Content-Type' => 'application/x-www-form-urlencoded' },
+        body: {
+          grant_type: 'refresh_token',
+          refresh_token: refresh_token
+        }
+      )
       if response.has_key? 'error' and response.has_key? 'error_description'
         err = "Error refreshing access token: "
         err << "#{response['error']} - #{response['error_description']}"
@@ -292,4 +301,4 @@ def handle_response(response) # :nodoc:
       end
     end
   end
-end
\ No newline at end of file
+end