diff --git a/sbb_binarize/ocrd-tool.json b/sbb_binarize/ocrd-tool.json
index 3095eeb..ec5e39d 100644
--- a/sbb_binarize/ocrd-tool.json
+++ b/sbb_binarize/ocrd-tool.json
@@ -19,7 +19,7 @@
         "model": {
           "description": "models directory.",
           "type": "string",
-          "required": true
+          "required": false
         }
       }
     }
diff --git a/sbb_binarize/ocrd_cli.py b/sbb_binarize/ocrd_cli.py
index df4daef..098da9c 100644
--- a/sbb_binarize/ocrd_cli.py
+++ b/sbb_binarize/ocrd_cli.py
@@ -37,6 +37,14 @@ class SbbBinarizeProcessor(Processor):
     def __init__(self, *args, **kwargs):
         kwargs['ocrd_tool'] = OCRD_TOOL['tools'][TOOL]
         kwargs['version'] = OCRD_TOOL['version']
+        if not(kwargs.get('show_help', None) or kwargs.get('dump_json', None) or kwargs.get('show_version')):
+            if not 'parameter' in kwargs:
+                kwargs['parameter'] = {}
+            if not 'model' in kwargs['parameter']:
+                if 'SBB_BINARIZE_DATA' in os.environ:
+                    kwargs['parameter']['model'] = os.environ['SBB_BINARIZE_DATA']
+                else:
+                    raise ValueError("Must pass 'model' parameter or set SBB_BINARIZE_DATA environment variable")
         super().__init__(*args, **kwargs)
 
     def process(self):