diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/challenge/Challenge.java b/acme4j-client/src/main/java/org/shredzone/acme4j/challenge/Challenge.java
index 740fa77e..aa67baf2 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/challenge/Challenge.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/challenge/Challenge.java
@@ -13,12 +13,8 @@
  */
 package org.shredzone.acme4j.challenge;
 
-import static java.util.stream.Collectors.toList;
-
 import java.net.URL;
 import java.time.Instant;
-import java.util.Collections;
-import java.util.List;
 import java.util.Objects;
 
 import org.shredzone.acme4j.AcmeJsonResource;
@@ -29,7 +25,6 @@ import org.shredzone.acme4j.connector.Connection;
 import org.shredzone.acme4j.exception.AcmeException;
 import org.shredzone.acme4j.exception.AcmeProtocolException;
 import org.shredzone.acme4j.toolbox.JSON;
-import org.shredzone.acme4j.toolbox.JSON.Array;
 import org.shredzone.acme4j.toolbox.JSONBuilder;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -51,7 +46,7 @@ public class Challenge extends AcmeJsonResource {
     protected static final String KEY_URL = "url";
     protected static final String KEY_STATUS = "status";
     protected static final String KEY_VALIDATED = "validated";
-    protected static final String KEY_ERRORS = "errors";
+    protected static final String KEY_ERROR = "error";
 
     /**
      * Creates a new generic {@link Challenge} object.
@@ -114,29 +109,12 @@ public class Challenge extends AcmeJsonResource {
     }
 
     /**
-     * Returns a list of reasons why the challenge has failed in the past, if returned by
-     * the server. New errors are always appended to the end of the list.
+     * Returns a reason why the challenge has failed in the past, if returned by the
+     * server. If there are multiple errors, they can be found in
+     * {@link Problem#getSubProblems()}.
      */
-    public List<Problem> getErrors() {
-        URL location = getLocation();
-        return Collections.unmodifiableList(getJSON().get(KEY_ERRORS)
-                    .asArray()
-                    .stream()
-                    .map(it -> it.asProblem(location))
-                    .collect(toList()));
-    }
-
-    /**
-     * Returns the last reason why the challenge has failed, if returned by the server.
-     * {@code null} if there are no errors.
-     */
-    public Problem getLastError() {
-        Array errors = getJSON().get(KEY_ERRORS).asArray();
-        if (!errors.isEmpty()) {
-            return errors.get(errors.size() - 1).asProblem(getLocation());
-        } else {
-            return null;
-        }
+    public Problem getError() {
+        return getJSON().get(KEY_ERROR).asProblem(getLocation());
     }
 
     /**
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/ChallengeTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/ChallengeTest.java
index a9acca4c..5911844d 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/ChallengeTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/challenge/ChallengeTest.java
@@ -26,7 +26,6 @@ import java.net.URISyntaxException;
 import java.net.URL;
 import java.time.Duration;
 import java.time.Instant;
-import java.util.List;
 
 import org.jose4j.lang.JoseException;
 import org.junit.Before;
@@ -102,21 +101,11 @@ public class ChallengeTest {
         assertThat(challenge.getJSON().get("notPresent").asString(), is(nullValue()));
         assertThat(challenge.getJSON().get("notPresentUrl").asURL(), is(nullValue()));
 
-        List<Problem> errors = challenge.getErrors();
-        assertThat(errors, is(notNullValue()));
-        assertThat(errors, hasSize(2));
-        assertThat(errors.get(0).getType(), is(URI.create("urn:ietf:params:acme:error:connection")));
-        assertThat(errors.get(0).getDetail(), is("connection refused"));
-        assertThat(errors.get(0).getInstance(), is(URI.create("http://example.com/documents/error.html")));
-        assertThat(errors.get(1).getType(), is(URI.create("urn:ietf:params:acme:error:incorrectResponse")));
-        assertThat(errors.get(1).getDetail(), is("bad token"));
-        assertThat(errors.get(1).getInstance(), is(URI.create("http://example.com/documents/faq.html")));
-
-        Problem lastError = challenge.getLastError();
-        assertThat(lastError, is(notNullValue()));
-        assertThat(lastError.getType(), is(URI.create("urn:ietf:params:acme:error:incorrectResponse")));
-        assertThat(lastError.getDetail(), is("bad token"));
-        assertThat(lastError.getInstance(), is(URI.create("http://example.com/documents/faq.html")));
+        Problem error = challenge.getError();
+        assertThat(error, is(notNullValue()));
+        assertThat(error.getType(), is(URI.create("urn:ietf:params:acme:error:incorrectResponse")));
+        assertThat(error.getDetail(), is("bad token"));
+        assertThat(error.getInstance(), is(URI.create("http://example.com/documents/faq.html")));
     }
 
     /**
diff --git a/acme4j-client/src/test/resources/json/genericChallenge.json b/acme4j-client/src/test/resources/json/genericChallenge.json
index 055143b4..2b3a4a12 100644
--- a/acme4j-client/src/test/resources/json/genericChallenge.json
+++ b/acme4j-client/src/test/resources/json/genericChallenge.json
@@ -3,16 +3,9 @@
   "status": "invalid",
   "url": "http://example.com/challenge/123",
   "validated": "2015-12-12T17:19:36.336785823Z",
-  "errors": [
-    {
-      "type": "urn:ietf:params:acme:error:connection",
-      "detail": "connection refused",
-      "instance": "/documents/error.html"
-    },
-    {
-      "type": "urn:ietf:params:acme:error:incorrectResponse",
-      "detail": "bad token",
-      "instance": "/documents/faq.html"
-    }
-  ]
+  "error": {
+    "type": "urn:ietf:params:acme:error:incorrectResponse",
+    "detail": "bad token",
+    "instance": "/documents/faq.html"
+  }
 }