diff --git a/index.php b/index.php
index 0251c003..04e4ffb4 100644
--- a/index.php
+++ b/index.php
@@ -1316,6 +1316,7 @@ public function isAuthenticated() {
 	if (isset($_POST['step'])) {
 		// mark step as failed
 		http_response_code(500);
+		header('Content-Type: application/json');
 		echo(json_encode(['proceed' => false, 'response' => $e->getMessage()]));
 		die();
 	}
@@ -1398,6 +1399,7 @@ public function isAuthenticated() {
 				break;
 		}
 		$updater->endStep($step);
+		header('Content-Type: application/json');
 		echo(json_encode(['proceed' => true]));
 	} catch (UpdateException $e) {
 		$message = $e->getData();
@@ -1413,6 +1415,7 @@ public function isAuthenticated() {
 			$updater->rollbackChanges($step);
 		}
 		http_response_code(500);
+		header('Content-Type: application/json');
 		echo(json_encode(['proceed' => false, 'response' => $message]));
 	} catch (\Exception $e) {
 		$message = $e->getMessage();
@@ -1428,6 +1431,7 @@ public function isAuthenticated() {
 			$updater->rollbackChanges($step);
 		}
 		http_response_code(500);
+		header('Content-Type: application/json');
 		echo(json_encode(['proceed' => false, 'response' => $message]));
 	}