diff --git a/maxkey-protocols/maxkey-protocol-oauth-2.0/src/main/java/org/maxkey/authz/oauth2/common/OAuth2Constants.java b/maxkey-protocols/maxkey-protocol-oauth-2.0/src/main/java/org/maxkey/authz/oauth2/common/OAuth2Constants.java
index 8d6b1f56..793b46d6 100644
--- a/maxkey-protocols/maxkey-protocol-oauth-2.0/src/main/java/org/maxkey/authz/oauth2/common/OAuth2Constants.java
+++ b/maxkey-protocols/maxkey-protocol-oauth-2.0/src/main/java/org/maxkey/authz/oauth2/common/OAuth2Constants.java
@@ -76,6 +76,7 @@ public class OAuth2Constants {
 		public static final String GRANT_TYPE_IMPLICIT            = "implicit";
 		public static final String GRANT_TYPE_AUTHORIZATION_CODE  = "authorization_code";
 		public static final String GRANT_TYPE_CLIENT_CREDENTIALS  = "client_credentials";
+		public static final String GRANT_TYPE_REFRESH_TOKEN		  = "refresh_token";
 		
 		
 		public static final String ACCESS_TOKEN           = "access_token";
diff --git a/maxkey-protocols/maxkey-protocol-oauth-2.0/src/main/java/org/maxkey/authz/oauth2/provider/endpoint/TokenEndpoint.java b/maxkey-protocols/maxkey-protocol-oauth-2.0/src/main/java/org/maxkey/authz/oauth2/provider/endpoint/TokenEndpoint.java
index 27329228..c4f60a60 100644
--- a/maxkey-protocols/maxkey-protocol-oauth-2.0/src/main/java/org/maxkey/authz/oauth2/provider/endpoint/TokenEndpoint.java
+++ b/maxkey-protocols/maxkey-protocol-oauth-2.0/src/main/java/org/maxkey/authz/oauth2/provider/endpoint/TokenEndpoint.java
@@ -230,11 +230,13 @@ public class TokenEndpoint extends AbstractEndpoint {
 	}
 
 	private boolean isRefreshTokenRequest(Map<String, String> parameters) {
-		return "refresh_token".equals(parameters.get(OAuth2Constants.PARAMETER.GRANT_TYPE)) && parameters.get("refresh_token") != null;
+		return OAuth2Constants.PARAMETER.GRANT_TYPE_REFRESH_TOKEN.equals(parameters.get(OAuth2Constants.PARAMETER.GRANT_TYPE)) 
+				&& parameters.get(OAuth2Constants.PARAMETER.GRANT_TYPE_REFRESH_TOKEN) != null;
 	}
 
 	private boolean isAuthCodeRequest(Map<String, String> parameters) {
-		return "authorization_code".equals(parameters.get(OAuth2Constants.PARAMETER.GRANT_TYPE)) && parameters.get(OAuth2Constants.PARAMETER.CODE) != null;
+		return OAuth2Constants.PARAMETER.GRANT_TYPE_AUTHORIZATION_CODE.equals(parameters.get(OAuth2Constants.PARAMETER.GRANT_TYPE)) 
+				&& parameters.get(OAuth2Constants.PARAMETER.CODE) != null;
 	}
 
 	public void setOAuth2RequestValidator(OAuth2RequestValidator oAuth2RequestValidator) {