diff --git a/common/certificate_checker.h b/common/certificate_checker.h
index bc675be..c785192 100644
--- a/common/certificate_checker.h
+++ b/common/certificate_checker.h
@@ -78,6 +78,9 @@
 enum class ServerToCheck {
   kUpdate = 0,
   kDownload,
+
+  // Ignore this server.
+  kNone,
 };
 
 // Responsible for checking whether update server certificates change, and
@@ -96,10 +99,8 @@
                                     CertificateCheckResult result) = 0;
   };
 
-  CertificateChecker(PrefsInterface* prefs,
-                     OpenSSLWrapper* openssl_wrapper,
-                     ServerToCheck server_to_check);
-  virtual ~CertificateChecker() = default;
+  CertificateChecker(PrefsInterface* prefs, OpenSSLWrapper* openssl_wrapper);
+  ~CertificateChecker();
 
   // This callback is called by libcurl just before the initialization of an
   // SSL connection after having processed all other SSL related options. Used
@@ -109,6 +110,11 @@
                                     SSL_CTX* ssl_ctx,
                                     void* cert_checker);
 
+  // Initialize this class as the singleton instance. Only one instance can be
+  // initialized at a time and it should be initialized before other methods
+  // can be used.
+  void Init();
+
   // Set the certificate observer to the passed instance. To remove the
   // observer, pass a nullptr. The |observer| instance must be valid while this
   // CertificateChecker verifies certificates.
@@ -120,24 +126,37 @@
   FRIEND_TEST(CertificateCheckerTest, ChangedCertificate);
   FRIEND_TEST(CertificateCheckerTest, FailedCertificate);
 
-  // This callback is called by openssl after initial SSL verification. It is
-  // used to perform any additional security verification on the connection,
-  // but we use them here to get hold of the server certificate, in order to
-  // determine if it has changed since the last connection. Since openssl forces
-  // us to do this statically, we pass a pointer to this instance via a
-  // thread-safe global pointer. The assigned callback is then called once per
+  // These callbacks are asynchronously called by openssl after initial SSL
+  // verification. They are used to perform any additional security verification
+  // on the connection, but we use them here to get hold of the server
+  // certificate, in order to determine if it has changed since the last
+  // connection. Since openssl forces us to do this statically, we define two
+  // different callbacks for the two different official update servers, and only
+  // assign the correspondent one. The assigned callback is then called once per
   // each certificate on the server and returns 1 for success and 0 for failure.
-  static int VerifySSLCallback(int preverify_ok, X509_STORE_CTX* x509_ctx);
+  static int VerifySSLCallbackDownload(int preverify_ok,
+                                       X509_STORE_CTX* x509_ctx);
+  static int VerifySSLCallbackUpdate(int preverify_ok,
+                                     X509_STORE_CTX* x509_ctx);
+  static int VerifySSLCallback(int preverify_ok,
+                               X509_STORE_CTX* x509_ctx,
+                               ServerToCheck server_to_check);
 
   // Checks if server certificate stored in |x509_ctx| has changed since last
-  // connection to that same server, specified by the |server_to_check_| member.
+  // connection to that same server, specified by |server_to_check|.
   // This is called by the callbacks defined above. The result of the
   // certificate check is passed to the observer, if any. Returns true on
   // success and false otherwise.
-  bool CheckCertificateChange(int preverify_ok, X509_STORE_CTX* x509_ctx);
+  bool CheckCertificateChange(int preverify_ok,
+                              X509_STORE_CTX* x509_ctx,
+                              ServerToCheck server_to_check);
 
   // Notifies the observer, if any, of a certificate checking.
-  void NotifyCertificateChecked(CertificateCheckResult result);
+  void NotifyCertificateChecked(ServerToCheck server_to_check,
+                                CertificateCheckResult result);
+
+  // The CertificateChecker singleton instance.
+  static CertificateChecker* cert_checker_singleton_;
 
   // Prefs instance used to store the certificates seen in the past.
   PrefsInterface* prefs_;
@@ -145,9 +164,6 @@
   // The wrapper for openssl operations.
   OpenSSLWrapper* openssl_wrapper_;
 
-  // The server to check from this certificate checker instance.
-  ServerToCheck server_to_check_;
-
   // The observer called whenever a certificate is checked, if not null.
   Observer* observer_{nullptr};