diff -Naur a/lib/Net/SNMP.pm b/lib/Net/SNMP.pm
--- a/lib/Net/SNMP.pm	2011-12-24 00:41:27.000000000 +0100
+++ b/lib/Net/SNMP.pm	2012-02-21 13:17:04.000000000 +0100
@@ -2564,7 +2564,7 @@
 
    if ($this->{_security}->discovered()) {
       DEBUG_INFO('discovery complete');
-      return $this->_discovery_complete();
+      $this->_discovery_complete();
    }
 
    # "If authenticated communication is required, then the discovery
@@ -2618,7 +2618,7 @@
    # assume that the synchronization has failed.
 
    if (($this->{_security}->discovered()) &&
-       ($this->{_error} =~ /usmStatsNotInTimeWindows/))
+       ((!$this->{_error}) || ($this->{_error} =~ /usmStatsNotInTimeWindows/)))
    {
       $this->_error_clear();
       DEBUG_INFO('discovery and synchronization complete');
diff -Naur a/lib/Net/SNMP/Security/USM.pm b/lib/Net/SNMP/Security/USM.pm
--- a/lib/Net/SNMP/Security/USM.pm	2011-12-24 00:41:27.000000000 +0100
+++ b/lib/Net/SNMP/Security/USM.pm	2012-02-21 13:20:47.000000000 +0100
@@ -471,6 +471,16 @@
       );
    }
 
+   # Synchronize the time
+   if (!$this->_synchronize($msg_engine_boots, $msg_engine_time)) {
+      return $this->_error();
+   }
+
+   # Check for timeliness
+   if (!defined $this->_timeliness($msg_engine_boots, $msg_engine_time)) {
+      return $this->_error();
+   }
+
    if ($security_level > SECURITY_LEVEL_NOAUTHNOPRIV) {
 
       # Authenticate the message
@@ -478,16 +488,6 @@
          return $this->_error();
       }
 
-      # Synchronize the time
-      if (!$this->_synchronize($msg_engine_boots, $msg_engine_time)) {
-         return $this->_error();
-      }
-
-      # Check for timeliness
-      if (!defined $this->_timeliness($msg_engine_boots, $msg_engine_time)) {
-         return $this->_error();
-      }
-
       if ($security_level > SECURITY_LEVEL_AUTHNOPRIV) {
 
          # Validate the msgPrivacyParameters length.