diff --git a/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/GitHubLogin.java b/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/GitHubLogin.java
index 0d66026..79cd552 100644
--- a/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/GitHubLogin.java
+++ b/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/GitHubLogin.java
@@ -126,7 +126,11 @@
 
     if (OAuthProtocol.isOAuthFinal(request)) {
       log.debug("Login-FINAL " + this);
-      login(oauth.loginPhase2(request, response));
+      AccessToken loginAccessToken = oauth.loginPhase2(request, response);
+      if(loginAccessToken != null && !loginAccessToken.isError()) {
+        login(loginAccessToken);
+      }
+
       if (isLoggedIn()) {
         log.debug("Login-SUCCESS " + this);
         response.sendRedirect(OAuthProtocol.getTargetUrl(request));
@@ -153,9 +157,9 @@
   }
 
   public GitHub login(AccessToken authToken) throws IOException {
-    log.debug("Logging in using access token {}", authToken.access_token);
+    log.debug("Logging in using access token {}", authToken.accessToken);
     this.token = authToken;
-    this.hub = GitHub.connectUsingOAuth(authToken.access_token);
+    this.hub = GitHub.connectUsingOAuth(authToken.accessToken);
     this.myself = hub.getMyself();
     return this.hub;
   }
diff --git a/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/GsonProvider.java b/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/GsonProvider.java
new file mode 100644
index 0000000..fd004c0
--- /dev/null
+++ b/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/GsonProvider.java
@@ -0,0 +1,31 @@
+// Copyright (C) 2014 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.googlesource.gerrit.plugins.github.oauth;
+
+import com.google.gson.FieldNamingPolicy;
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.inject.Provider;
+import com.google.inject.Singleton;
+
+@Singleton
+public class GsonProvider implements Provider<Gson> {
+
+  @Override
+  public Gson get() {
+    return new GsonBuilder().setFieldNamingPolicy(
+        FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES).create();
+  }
+}
diff --git a/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthProtocol.java b/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthProtocol.java
index fae8219..61f4890 100644
--- a/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthProtocol.java
+++ b/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthProtocol.java
@@ -1,10 +1,12 @@
 package com.googlesource.gerrit.plugins.github.oauth;
 
 import java.io.IOException;
+import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.io.UnsupportedEncodingException;
 import java.net.HttpURLConnection;
 import java.net.URLEncoder;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Set;
@@ -25,13 +27,14 @@
 
 import com.google.common.base.Charsets;
 import com.google.common.base.Strings;
+import com.google.common.io.CharStreams;
 import com.google.gson.Gson;
 import com.google.inject.Inject;
 import com.google.inject.Singleton;
 
 @Singleton
 public class OAuthProtocol {
-  
+
   public static enum Scope {
     DEFAULT(""),
     USER("user"),
@@ -63,8 +66,11 @@
   private final Gson gson;
 
   public static class AccessToken {
-    public String access_token;
-    public String token_type;
+    public String accessToken;
+    public String tokenType;
+    public String error;
+    public String errorDescription;
+    public String errorUri;
 
     public AccessToken() {
     }
@@ -75,14 +81,19 @@
 
     public AccessToken(String token, String type, Scope... scopes) {
       this();
-      this.access_token = token;
-      this.token_type = type;
+      this.accessToken = token;
+      this.tokenType = type;
     }
 
     @Override
     public String toString() {
-      return "AccessToken [access_token=" + access_token + ", token_type="
-          + token_type + "]";
+      if (isError()) {
+        return "Error AccessToken [error=" + error + ", error_description="
+            + errorDescription + ", error_uri=" + errorUri + "]";
+      } else {
+        return "AccessToken [access_token=" + accessToken + ", token_type="
+            + tokenType + "]";
+      }
     }
 
     @Override
@@ -91,9 +102,9 @@
       int result = 1;
       result =
           prime * result
-              + ((access_token == null) ? 0 : access_token.hashCode());
+              + ((accessToken == null) ? 0 : accessToken.hashCode());
       result =
-          prime * result + ((token_type == null) ? 0 : token_type.hashCode());
+          prime * result + ((tokenType == null) ? 0 : tokenType.hashCode());
       return result;
     }
 
@@ -103,21 +114,29 @@
       if (obj == null) return false;
       if (getClass() != obj.getClass()) return false;
       AccessToken other = (AccessToken) obj;
-      if (access_token == null) {
-        if (other.access_token != null) return false;
-      } else if (!access_token.equals(other.access_token)) return false;
-      if (token_type == null) {
-        if (other.token_type != null) return false;
-      } else if (!token_type.equals(other.token_type)) return false;
+      if (accessToken == null) {
+        if (other.accessToken != null) return false;
+      } else if (!accessToken.equals(other.accessToken)) return false;
+      if (tokenType == null) {
+        if (other.tokenType != null) return false;
+      } else if (!tokenType.equals(other.tokenType)) return false;
       return true;
     }
+
+    public boolean isError() {
+      return !Strings.isNullOrEmpty(error);
+    }
   }
 
   @Inject
-  public OAuthProtocol(GitHubOAuthConfig config, GitHubHttpProvider httpClientProvider, Gson gson) {
+  public OAuthProtocol(GitHubOAuthConfig config, GitHubHttpProvider httpClientProvider,
+      /* We need to explicitly tell Guice which Provider<> we need as this class may be
+         instantiated outside the standard Guice Module set-up (e.g. initial Servlet login
+         filter) */
+      GsonProvider gsonProvider) {
     this.config = config;
     this.http = httpClientProvider.get();
-    this.gson = gson;
+    this.gson = gsonProvider.get();
   }
 
   public void loginPhase1(HttpServletRequest request,
@@ -195,21 +214,23 @@
         LOG.error("POST " + config.gitHubOAuthAccessTokenUrl
             + " request for access token failed with status "
             + postResponse.getStatusLine());
-        response.sendError(HttpURLConnection.HTTP_UNAUTHORIZED,
-            "Request for access token not authorised");
         EntityUtils.consume(postResponse.getEntity());
         return null;
       }
 
-      AccessToken token =
-          gson.fromJson(new InputStreamReader(postResponse.getEntity()
-              .getContent(), "UTF-8"), AccessToken.class);
+      InputStream content = postResponse.getEntity().getContent();
+      String tokenJsonString =
+          CharStreams.toString(new InputStreamReader(content,
+              StandardCharsets.UTF_8));
+      AccessToken token = gson.fromJson(tokenJsonString, AccessToken.class);
+      if (token.isError()) {
+        LOG.error("POST " + config.gitHubOAuthAccessTokenUrl
+            + " returned an error token: " + token);
+      }
       return token;
     } catch (IOException e) {
       LOG.error("POST " + config.gitHubOAuthAccessTokenUrl
           + " request for access token failed", e);
-      response.sendError(HttpURLConnection.HTTP_UNAUTHORIZED,
-          "Request for access token not authorised");
       return null;
     }
   }
diff --git a/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthWebFilter.java b/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthWebFilter.java
index f546753..a8823a9 100644
--- a/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthWebFilter.java
+++ b/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthWebFilter.java
@@ -92,7 +92,7 @@
               new AuthenticatedHttpRequest(httpRequest, config.httpHeader,
                   ghLogin.getMyself().getLogin(),
                   config.oauthHttpHeader,
-                  GITHUB_EXT_ID + ghLogin.getToken().access_token);
+                  GITHUB_EXT_ID + ghLogin.getToken().accessToken);
         }
 
         if (OAuthProtocol.isOAuthFinalForOthers(httpRequest)) {
@@ -125,7 +125,7 @@
       String user = myself.getLogin();
 
       updateSecureConfigWithRetry(ghLogin.hub.getMyOrganizations().keySet(),
-          user, ghLogin.token.access_token);
+          user, ghLogin.token.accessToken);
     }
   }
 
diff --git a/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/git/GitHubRepository.java b/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/git/GitHubRepository.java
index 7722d63..a677958 100644
--- a/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/git/GitHubRepository.java
+++ b/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/git/GitHubRepository.java
@@ -42,7 +42,7 @@
 
   public String getCloneUrl() {
     return cloneUrl.replace("://", "://" + ghLogin.getMyself().getLogin() + ":"
-        + ghLogin.getToken().access_token + "@");
+        + ghLogin.getToken().accessToken + "@");
   }
 
   public String getOrganisation() {
diff --git a/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/git/ReplicateProjectStep.java b/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/git/ReplicateProjectStep.java
index d4b52e8..3881c86 100644
--- a/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/git/ReplicateProjectStep.java
+++ b/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/git/ReplicateProjectStep.java
@@ -48,7 +48,7 @@
     this.replicationConfig = replicationConfig;
     GitHubLogin ghLogin = ghLoginProvider.get();
     this.authUsername = ghLogin.getMyself().getLogin();
-    this.authToken = ghLogin.getToken().access_token;
+    this.authToken = ghLogin.getToken().accessToken;
     this.gitHubUrl = gitHubUrl;
   }