diff --git a/eobuilder/cmdline.py b/eobuilder/cmdline.py
index 95e916b..733e8be 100644
--- a/eobuilder/cmdline.py
+++ b/eobuilder/cmdline.py
@@ -136,10 +136,10 @@ def output(cmd, print_output=False, exit_on_error=True):
                 stderr=subprocess.STDOUT,
                 shell=True)
     except subprocess.CalledProcessError as e:
-        sys.stderr.write(e.output)
+        if e.output:
+            sys.stderr.write(e.output.decode('utf-8'))
         if exit_on_error:
             error(cmd)
     if print_output:
         print(output)
-    return output.decode('utf-8')
-
+    return output.decode('utf-8') if output else None