diff --git a/advertools/logs.py b/advertools/logs.py
index 28757776..8e63ce3c 100644
--- a/advertools/logs.py
+++ b/advertools/logs.py
@@ -544,7 +544,11 @@ def logs_to_df(
         raise ValueError(
             "Please provide an `output_file` with a `.parquet` " "extension."
         )
-
+    if not LOG_DATE_FORMATS.get(log_format) and fields is None:
+        raise ValueError(
+            "Please supply a value for the `fields` parameter when you provide a custom"
+            "log format."
+        )
     regex = LOG_FORMATS.get(log_format) or log_format
     date_fmt = date_format or LOG_DATE_FORMATS.get(log_format)
     columns = fields or LOG_FIELDS[log_format]
diff --git a/tests/test_logs.py b/tests/test_logs.py
index a2f8130f..e4f5124f 100644
--- a/tests/test_logs.py
+++ b/tests/test_logs.py
@@ -146,4 +146,16 @@ def test_logstodf_parses_raises_wrong_date_fmt():
             date_format="%B %, M:%S %z",
         )
         result = pd.read_parquet(path / "delete_output.parquet")
-        assert not ("datetime" in result["datetime"].dtype.name)
+        assert "datetime" not in result["datetime"].dtype.name
+
+
+def test_logstodf_raises_on_no_fields():
+    """Raise an exception if user proivides custom log format without fields."""
+    with pytest.raises(ValueError):
+        logs_to_df(
+            log_file="some_file.txt",
+            output_file="output_file.parquet",
+            errors_file="errors.txt",
+            log_format="custom_regex",
+            fields=None,
+        )