diff --git a/src/caoscrawler/converters.py b/src/caoscrawler/converters.py
index 51dc5615ee097e44c03e60df06239f89f8399f9a..7150db751f429e2397df878487d165cc9e451866 100644
--- a/src/caoscrawler/converters.py
+++ b/src/caoscrawler/converters.py
@@ -446,7 +446,7 @@ class Converter(object, metaclass=ABCMeta):
                 match = SINGLE_VAR_RE.match(transformer["out"])
                 if match is None:
                     raise RuntimeError("'out' of the transformer definition must specify a single"
-                                       " variable name")
+                                       f" variable name. It was {transformer['out']}")
                 print(f"set {match.group('varname')} to {out_value}")
                 values[match.group('varname')] = out_value
 
diff --git a/src/caoscrawler/scanner.py b/src/caoscrawler/scanner.py
index 5b1d9e511fea0183a81e14c0077a9284efe8ed02..25f72e56d460a2e0c8481ba7c5dc2818937ad4fa 100644
--- a/src/caoscrawler/scanner.py
+++ b/src/caoscrawler/scanner.py
@@ -211,7 +211,7 @@ def create_transformer_registry(definition: dict):
             }
 
     # Load modules and associate classes:
-    for key, value in transformer_registry.items():
+    for key, value in transformer_def.items():
         module = importlib.import_module(value["package"])
         registry[key] = getattr(module, value["function"])
     return registry
diff --git a/unittests/test_directories/test_transformers/cfood.yml b/unittests/test_directories/test_transformers/cfood.yml
index 84066a4c953bacd757398207ff9bf601fa0a6564..9208d62c717e2435417f2bda54592dbaa57c332f 100644
--- a/unittests/test_directories/test_transformers/cfood.yml
+++ b/unittests/test_directories/test_transformers/cfood.yml
@@ -11,7 +11,7 @@ RootDir:
       transform:
         MakeDayLong:
           in: $day_short
-          out: day_long  # no dollar sign here, because this is a variable name and no expression
+          out: $day_long
           functions:
           - ifelse:  # name of the function
               match: Mon  # match is one specific argument
@@ -21,7 +21,7 @@ RootDir:
               then: Tuesday
         TestSplit:
           in: $day_short
-          out: day_split  # no dollar sign here, because this is a variable name and no expression
+          out: $day_split
           functions:
           - split:
               marker: o