diff --git a/attributs.py b/attributs.py
index 3aeffc6..c8173f6 100644
--- a/attributs.py
+++ b/attributs.py
@@ -1517,13 +1517,16 @@ class certificat(Attr):
 
     def _format_cert(self, certificat):
             import OpenSSL
-            if certificat.startswith('-----BEGIN CERTIFICATE-----'):
-                certificat = ssl.PEM_cert_to_DER_cert(certificat)
             try:
+                if certificat.startswith('-----BEGIN CERTIFICATE-----'):
+                    certificat = ssl.PEM_cert_to_DER_cert(certificat)
                 x509 = OpenSSL.crypto.load_certificate(OpenSSL.crypto.FILETYPE_ASN1, certificat)
-            except:
-                certificat = base64.b64decode(certificat)
-                x509 = OpenSSL.crypto.load_certificate(OpenSSL.crypto.FILETYPE_ASN1, certificat)
+            except Exception:
+                try:
+                    certificat = base64.b64decode(certificat)
+                    x509 = OpenSSL.crypto.load_certificate(OpenSSL.crypto.FILETYPE_ASN1, certificat)
+                except Exception:
+                    raise ValueError("Format du certificat invalide, est-il bien au format DER ou PEM ?")
             data = {}
             data['subject'] = dict(x509.get_subject().get_components())
             data['issuer'] = dict(x509.get_issuer().get_components())