diff --git a/check_xbps.py b/check_xbps.py
index c3d3679..5b7d93d 100755
--- a/check_xbps.py
+++ b/check_xbps.py
@@ -88,7 +88,7 @@ def run_command(cmdline):
 				stderr = subprocess.PIPE
 			)
 	except OSError:
-		plugin.back2nagios(3, 'Could not execute command line: %s' % subprocess.list2cmdline(cmdline))
+		plugin.back2nagios(plugin.RETURNCODE['UNKNOWN'], 'Could not execute command line: %s' % subprocess.list2cmdline(cmdline))
 
 	(sout,serr) = cmd.communicate()
 	plugin.verbose(2, 'Runtime %.3fs' % (time.time() - tstart, ) )
@@ -112,7 +112,7 @@ if plugin.options.sync_repo_index:
 	serr and plugin.verbose(3, serr, prefix='stderr: ')
 	plugin.verbose(2, 'Return code: %d' % rc)
 	if rc != 0 and plugin.options.fail_on_sync_failure:
-		plugin.back2nagios(2, 'Syncing of repository index files failed')
+		plugin.back2nagios(plugin.RETURNCODE['CRITICAL'], 'Syncing of repository index files failed')
 
 ##############################################################################
 
@@ -122,6 +122,14 @@ sout and plugin.verbose(3, sout, prefix='stdout: ')
 serr and plugin.verbose(3, serr, prefix='stderr: ')
 plugin.verbose(2, 'Return code: %d' % rc)
 
+if rc == 8:
+	# RC  8: Transaction aborted due to unresolved shlibs.
+	plugin.back2nagios(plugin.RETURNCODE['WARNING'], serr[-1], serr[:-1])
+elif rc not in [0, 6]:
+	# RC  0: Packages to update
+	# RC  6: Package(s) already installed
+	plugin.back2nagios(plugin.RETURNCODE['WARNING'], 'Unknown returncode "%s", please contact the author of plugin or open an issue!' % rc)
+
 action = {'remove':[], 'update':[], 'install':[],}
 arch = {}
 repo = {}
@@ -182,7 +190,7 @@ else:
 		stats += '%s from %s, ' % (v, k)
 	multiline.append(stats[:-2])
 
-	plugin.remember_check('Updates', plugin.RETURNCODE['WARNING'], out, multilineoutput=multiline)
+	plugin.remember_check('Updates', plugin.RETURNCODE['CRITICAL'], out, multilineoutput=multiline)
 
 # Exit
 plugin.brain2output()