diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/challenge/OutOfBand01Challenge.java b/acme4j-client/src/main/java/org/shredzone/acme4j/challenge/OutOfBand01Challenge.java
index 55dcbeac..6a033852 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/challenge/OutOfBand01Challenge.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/challenge/OutOfBand01Challenge.java
@@ -46,7 +46,7 @@ public class OutOfBand01Challenge extends Challenge {
      */
     public URL getValidationUrl() {
         try {
-            return new URL((String) get("url"));
+            return new URL((String) get("href"));
         } catch (MalformedURLException ex) {
             throw new AcmeProtocolException("Invalid validation URL", ex);
         }
diff --git a/acme4j-client/src/test/resources/json.properties b/acme4j-client/src/test/resources/json.properties
index 908e1445..d9aae368 100644
--- a/acme4j-client/src/test/resources/json.properties
+++ b/acme4j-client/src/test/resources/json.properties
@@ -235,7 +235,7 @@ tlsSni02Challenge = \
 oobChallenge = \
   { \
     "type": "oob-01", \
-    "url": "https://example.com/validate/evaGxfADs6pSRb2LAv9IZ" \
+    "href": "https://example.com/validate/evaGxfADs6pSRb2LAv9IZ" \
   }
 
 #
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