diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/connector/DefaultConnection.java b/acme4j-client/src/main/java/org/shredzone/acme4j/connector/DefaultConnection.java
index 3f3a4c8f..2947187a 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/connector/DefaultConnection.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/connector/DefaultConnection.java
@@ -56,6 +56,11 @@ import org.slf4j.LoggerFactory;
 public class DefaultConnection implements Connection {
     private static final Logger LOG = LoggerFactory.getLogger(DefaultConnection.class);
 
+    public static final String ACME_ERROR_PREFIX = "urn:ietf:params:acme:error:";
+
+    @Deprecated
+    public static final String ACME_ERROR_PREFIX_DEPRECATED = "urn:acme:error:";
+
     private static final Pattern BASE64URL_PATTERN = Pattern.compile("[0-9A-Za-z_-]+");
 
     protected final HttpConnector httpConnector;
@@ -313,12 +318,12 @@ public class DefaultConnection implements Connection {
             }
 
             switch (type) {
-                case "urn:acme:error:unauthorized":
-                case "urn:ietf:params:acme:error:unauthorized":
+                case ACME_ERROR_PREFIX + "unauthorized":
+                case ACME_ERROR_PREFIX_DEPRECATED + "unauthorized":
                     throw new AcmeUnauthorizedException(type, detail);
 
-                case "urn:acme:error:rateLimited":
-                case "urn:ietf:params:acme:error:rateLimited":
+                case ACME_ERROR_PREFIX + "rateLimited":
+                case ACME_ERROR_PREFIX_DEPRECATED + "rateLimited":
                     throw new AcmeRateLimitExceededException(type, detail, getRetryAfterHeader());
 
                 default:
diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeServerException.java b/acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeServerException.java
index 4ff648ee..7b40effe 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeServerException.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeServerException.java
@@ -13,6 +13,8 @@
  */
 package org.shredzone.acme4j.exception;
 
+import org.shredzone.acme4j.connector.DefaultConnection;
+
 /**
  * An exception that is thrown when the ACME server returned an error. It contains
  * further details of the cause.
@@ -20,9 +22,6 @@ package org.shredzone.acme4j.exception;
 public class AcmeServerException extends AcmeException {
     private static final long serialVersionUID = 5971622508467042792L;
 
-    private static final String ACME_ERROR_PREFIX = "urn:ietf:params:acme:error:";
-    private static final String ACME_ERROR_PREFIX_DEPRECATED = "urn:acme:error:";
-
     private final String type;
 
     /**
@@ -56,11 +55,12 @@ public class AcmeServerException extends AcmeException {
      * @return ACME error type, or {@code null} if this is not an
      *         {@code "urn:ietf:params:acme:error"}
      */
+    @SuppressWarnings("deprecation")
     public String getAcmeErrorType() {
-        if (type.startsWith(ACME_ERROR_PREFIX)) {
-            return type.substring(ACME_ERROR_PREFIX.length());
-        } else if (type.startsWith(ACME_ERROR_PREFIX_DEPRECATED)) {
-            return type.substring(ACME_ERROR_PREFIX_DEPRECATED.length());
+        if (type.startsWith(DefaultConnection.ACME_ERROR_PREFIX)) {
+            return type.substring(DefaultConnection.ACME_ERROR_PREFIX.length());
+        } else if (type.startsWith(DefaultConnection.ACME_ERROR_PREFIX_DEPRECATED)) {
+            return type.substring(DefaultConnection.ACME_ERROR_PREFIX_DEPRECATED.length());
         } else {
             return null;
         }