diff --git a/src/ReCaptcha/RequestMethod/CurlPost.php b/src/ReCaptcha/RequestMethod/CurlPost.php
index 5ff831a..f38561c 100644
--- a/src/ReCaptcha/RequestMethod/CurlPost.php
+++ b/src/ReCaptcha/RequestMethod/CurlPost.php
@@ -42,6 +42,7 @@
 use ReCaptcha\ReCaptcha;
 use ReCaptcha\RequestMethod;
 use ReCaptcha\RequestParameters;
+use ReCaptcha\Response;
 
 /**
  * Sends cURL request to the reCAPTCHA service.
@@ -98,7 +99,7 @@ public function submit(RequestParameters $params): string
                 return $response;
             }
 
-            return '{"success": false, "error-codes": ["'.ReCaptcha::E_CONNECTION_FAILED.'"]}';
+            return Response::errorJson(ReCaptcha::E_CONNECTION_FAILED);
         } finally {
             curl_close($handle);
         }
diff --git a/src/ReCaptcha/RequestMethod/Post.php b/src/ReCaptcha/RequestMethod/Post.php
index 77ff691..46d0c97 100644
--- a/src/ReCaptcha/RequestMethod/Post.php
+++ b/src/ReCaptcha/RequestMethod/Post.php
@@ -42,6 +42,7 @@
 use ReCaptcha\ReCaptcha;
 use ReCaptcha\RequestMethod;
 use ReCaptcha\RequestParameters;
+use ReCaptcha\Response;
 
 /**
  * Sends POST requests to the reCAPTCHA service.
@@ -87,6 +88,6 @@ public function submit(RequestParameters $params): string
             return $response;
         }
 
-        return '{"success": false, "error-codes": ["'.ReCaptcha::E_CONNECTION_FAILED.'"]}';
+        return Response::errorJson(ReCaptcha::E_CONNECTION_FAILED);
     }
 }
diff --git a/src/ReCaptcha/RequestMethod/SocketPost.php b/src/ReCaptcha/RequestMethod/SocketPost.php
index 955a49d..32e9e6e 100644
--- a/src/ReCaptcha/RequestMethod/SocketPost.php
+++ b/src/ReCaptcha/RequestMethod/SocketPost.php
@@ -42,6 +42,7 @@
 use ReCaptcha\ReCaptcha;
 use ReCaptcha\RequestMethod;
 use ReCaptcha\RequestParameters;
+use ReCaptcha\Response;
 
 /**
  * Sends a POST request to the reCAPTCHA service, but makes use of fsockopen()
@@ -76,17 +77,17 @@ public function submit(RequestParameters $params): string
         $urlParsed = parse_url($this->siteVerifyUrl);
 
         if (false === $urlParsed || !isset($urlParsed['host']) || !isset($urlParsed['path'])) {
-            return '{"success": false, "error-codes": ["'.ReCaptcha::E_CONNECTION_FAILED.'"]}';
+            return Response::errorJson(ReCaptcha::E_CONNECTION_FAILED);
         }
 
         $handle = fsockopen('ssl://'.$urlParsed['host'], 443, $errno, $errstr, 30);
 
         if (false === $handle || 0 !== $errno || '' !== $errstr) {
-            return '{"success": false, "error-codes": ["'.ReCaptcha::E_CONNECTION_FAILED.'"]}';
+            return Response::errorJson(ReCaptcha::E_CONNECTION_FAILED);
         }
 
         if (false === stream_set_timeout($handle, 60)) {
-            return '{"success": false, "error-codes": ["'.ReCaptcha::E_CONNECTION_FAILED.'"]}';
+            return Response::errorJson(ReCaptcha::E_CONNECTION_FAILED);
         }
 
         $content = $params->toQueryString();
@@ -108,13 +109,13 @@ public function submit(RequestParameters $params): string
         }
 
         if (1 !== preg_match('#^HTTP/1\.[01] 200 OK#', $response)) {
-            return '{"success": false, "error-codes": ["'.ReCaptcha::E_BAD_RESPONSE.'"]}';
+            return Response::errorJson(ReCaptcha::E_BAD_RESPONSE);
         }
 
         $parts = preg_split("#\n\\s*\n#Uis", $response);
 
         if (!is_array($parts) || !isset($parts[1])) {
-            return '{"success": false, "error-codes": ["'.ReCaptcha::E_BAD_RESPONSE.'"]}';
+            return Response::errorJson(ReCaptcha::E_BAD_RESPONSE);
         }
 
         return $parts[1];
diff --git a/src/ReCaptcha/Response.php b/src/ReCaptcha/Response.php
index 852439b..da37c4b 100644
--- a/src/ReCaptcha/Response.php
+++ b/src/ReCaptcha/Response.php
@@ -97,6 +97,18 @@ public function __construct(bool $success, array $errorCodes = [], string $hostn
         $this->errorCodes = $errorCodes;
     }
 
+    /**
+     * Build an error response JSON string with the specified error code.
+     *
+     * @param string $errorCode The error code to return
+     *
+     * @return string The JSON string
+     */
+    public static function errorJson(string $errorCode): string
+    {
+        return json_encode(['success' => false, 'error-codes' => [$errorCode]]);
+    }
+
     /**
      * Build the response from the expected JSON returned by the service.
      */