diff --git a/src/attributecode/cmd.py b/src/attributecode/cmd.py
index 3f61b89c..53d78156 100644
--- a/src/attributecode/cmd.py
+++ b/src/attributecode/cmd.py
@@ -932,6 +932,21 @@ def transform(location, output, configuration, worksheet, quiet, verbose):  # NO
     elif location.endswith(".xlsx"):
         new_data, errors = transform_excel(location, worksheet)
 
+    data_keys = new_data[0].keys() if new_data else []
+    transformer_keys = transformer.field_renamings.keys()
+    dup_keys = []
+
+    for key in transformer_keys:
+        if key in data_keys:
+            dup_keys.append(key)
+
+    if dup_keys:
+        msg = "The following field(s) in the input data are duplicated in the transformer field renamings: {dup_keys}.\nPlease correct and re-run.".format(
+            **locals()
+        )
+        click.echo(msg)
+        sys.exit(1)
+
     if not errors:
         updated_data, errors = transform_data(new_data, transformer)