diff --git a/src/Symfony/Component/Mailer/Bridge/Mailgun/Http/Api/MailgunTransport.php b/src/Symfony/Component/Mailer/Bridge/Mailgun/Http/Api/MailgunTransport.php
index 9da64c4e2b..ac06c005cd 100644
--- a/src/Symfony/Component/Mailer/Bridge/Mailgun/Http/Api/MailgunTransport.php
+++ b/src/Symfony/Component/Mailer/Bridge/Mailgun/Http/Api/MailgunTransport.php
@@ -58,9 +58,11 @@ class MailgunTransport extends AbstractApiTransport
         ]);
 
         if (200 !== $response->getStatusCode()) {
-            $error = $response->toArray(false);
+            if ('application/json' === $response->getHeaders(false)['content-type'][0]) {
+                throw new TransportException(sprintf('Unable to send an email: %s (code %s).', $response->toArray(false)['message'], $response->getStatusCode()));
+            }
 
-            throw new TransportException(sprintf('Unable to send an email: %s (code %s).', $error['message'], $response->getStatusCode()));
+            throw new TransportException(sprintf('Unable to send an email: %s (code %s).', $response->getContent(false), $response->getStatusCode()));
         }
     }
 
diff --git a/src/Symfony/Component/Mailer/Bridge/Mailgun/Http/MailgunTransport.php b/src/Symfony/Component/Mailer/Bridge/Mailgun/Http/MailgunTransport.php
index 1cc0f25dec..819460ba40 100644
--- a/src/Symfony/Component/Mailer/Bridge/Mailgun/Http/MailgunTransport.php
+++ b/src/Symfony/Component/Mailer/Bridge/Mailgun/Http/MailgunTransport.php
@@ -59,9 +59,11 @@ class MailgunTransport extends AbstractHttpTransport
         ]);
 
         if (200 !== $response->getStatusCode()) {
-            $error = $response->toArray(false);
+            if ('application/json' === $response->getHeaders(false)['content-type'][0]) {
+                throw new TransportException(sprintf('Unable to send an email: %s (code %s).', $response->toArray(false)['message'], $response->getStatusCode()));
+            }
 
-            throw new TransportException(sprintf('Unable to send an email: %s (code %s).', $error['message'], $response->getStatusCode()));
+            throw new TransportException(sprintf('Unable to send an email: %s (code %s).', $response->getContent(false), $response->getStatusCode()));
         }
     }
 }