diff --git a/osc/connection.py b/osc/connection.py
index 7a8b37de..379799a7 100644
--- a/osc/connection.py
+++ b/osc/connection.py
@@ -668,6 +668,9 @@ class SignatureAuthHandler(AuthHandlerBase):
     def ssh_sign(self, data, namespace, keyfile=None):
         if not keyfile:
             keyfile = self.guess_keyfile()
+        if not keyfile:
+            raise oscerr.OscIOError(None, "No SSH key configured or auto-detected")
+        keyfile = os.path.expanduser(keyfile)
         cmd = [self.ssh_keygen_path, '-Y', 'sign', '-f', keyfile, '-n', namespace, '-q']
         proc = subprocess.Popen(cmd, stdin=subprocess.PIPE, stdout=subprocess.PIPE, encoding="utf-8")
         signature, _ = proc.communicate(data)