diff --git a/api/tests/api/CreateUserFailsIfKeyKnowledgeHeaderIsNotSetCept.php b/api/tests/api/CreateUserFailsIfKeyKnowledgeHeaderIsNotSetCept.php
index 838ccec..4f30de9 100644
--- a/api/tests/api/CreateUserFailsIfKeyKnowledgeHeaderIsNotSetCept.php
+++ b/api/tests/api/CreateUserFailsIfKeyKnowledgeHeaderIsNotSetCept.php
@@ -15,7 +15,7 @@ $I = new ApiTester($scenario);
 $I->wantTo('see that create a new user fails if key knowledge header is not set');
 $I->sendPOST('/users', $userJson);
 $I->seeResponseCodeIs(500);
-$I->seeResponseIsJson();
+$I->seeResponseEquals('');
 
 try {
   $result = file_get_contents($usersDir . '0');
diff --git a/api/tests/api/CreateUserFailsIfKeyKnowledgeIsNotProvedCept.php b/api/tests/api/CreateUserFailsIfKeyKnowledgeIsNotProvedCept.php
index 51e4af7..e8f64b3 100644
--- a/api/tests/api/CreateUserFailsIfKeyKnowledgeIsNotProvedCept.php
+++ b/api/tests/api/CreateUserFailsIfKeyKnowledgeIsNotProvedCept.php
@@ -16,7 +16,7 @@ $I->wantTo('see that create a new user fails if key knowledge is wrong');
 $I->haveHTTPHeader('X-Croodle-Proof-Key-Knowledge', $wrongKeyKnowledge);
 $I->sendPOST('/users', $userJson);
 $I->seeResponseCodeIs(500);
-$I->seeResponseIsJson();
+$I->seeResponseEquals('');
 
 try {
   $result = file_get_contents($usersDir . '0');