--- a/base/univention-updater/modules/univention/updater/tools.py	
+++ a/base/univention-updater/modules/univention/updater/tools.py	
@@ -42,6 +42,7 @@ from commands import (
     cmd_update,
 )
 from errors import (
+    UpdaterException,
     CannotResolveComponentServerError,
     ConfigurationError,
     DownloadError,
@@ -1167,10 +1168,10 @@ class UniventionUpdater:
             stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)
         (stdout, stderr) = p1.communicate()
         ud.debug(ud.NETWORK, ud.PROCESS, 'check for updates with "dist-upgrade -s", the returncode is %d' % p1.returncode)
-        if p1.returncode == 100:
-            print stderr
         ud.debug(ud.NETWORK, ud.PROCESS, 'stderr=%s' % stderr)
         ud.debug(ud.NETWORK, ud.INFO, 'stdout=%s' % stdout)
+        if p1.returncode == 100:
+            raise UpdaterException(stderr)
 
         new_packages = []
         upgraded_packages = []
--- a/doc/errata/staging/univention-updater.yaml	
+++ a/doc/errata/staging/univention-updater.yaml	
@@ -3,8 +3,9 @@ release: "4.3"
 version: [2]
 scope: ucs_4.3-0-errata4.3-2
 src: univention-updater
-fix: 13.0.1-61A~4.3.0.201810120915 
+fix: 13.0.1-61A~4.3.0.201810120915
 desc: |
  This update addresses the following issue(s):
- * Fixes non existing error message in univention-updater
+ * In case univention-updater detects a problem while checking for updatable
+   packages, it now prints the error message provided by apt-get.
 bug: [34444]