diff --git a/HISTORY.rst b/HISTORY.rst
index 615e5ce..ade7552 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -6,6 +6,8 @@ History
 0.10.x (2019-XX-XX)
 ------------------
 * Documentation: Added a "Peer Comparison Analysis" Jupyter Notebook under "/examples" (@i3creations #197)
+* Minor: Update error message to clarify multiple tickers only work with single metrics
+* Updated development dependencies
 
 
 0.9.x (2019-01-30)
diff --git a/tests/test_tiingo.py b/tests/test_tiingo.py
index 0d0da23..9d920c2 100644
--- a/tests/test_tiingo.py
+++ b/tests/test_tiingo.py
@@ -6,7 +6,7 @@ from unittest import TestCase
 import vcr
 
 from tiingo import TiingoClient
-from tiingo.api import InvalidFrequencyError
+from tiingo.exceptions import InvalidFrequencyError
 from tiingo.restclient import RestClientError
 
 
diff --git a/tests/test_tiingo_pandas.py b/tests/test_tiingo_pandas.py
index 54ed91e..7d22ba7 100644
--- a/tests/test_tiingo_pandas.py
+++ b/tests/test_tiingo_pandas.py
@@ -4,7 +4,7 @@
 import vcr
 from unittest import TestCase
 from tiingo import TiingoClient
-from tiingo.api import APIColumnNameError, InstallPandasException
+from tiingo.exceptions import APIColumnNameError, InstallPandasException, MissingRequiredArgumentError
 try:
     import pandas as pd
     pandas_is_installed = True
@@ -69,6 +69,10 @@ class TestTiingoWithPython(TestCase):
             self._client.get_dataframe(['GOOGL', 'AAPL'], startDate='2018-01-05',
                                                 endDate='2018-01-19', metric_name='xopen', frequency='weekly')
 
+    def test_metric_name_missing_when_multiple_tickers(self):
+        with self.assertRaises(MissingRequiredArgumentError):
+            self._client.get_dataframe(['GOOGL', 'AAPL'], frequency='weekly')
+
     @vcr.use_cassette('tests/fixtures/ticker_price_pandas_single.yaml')
     def test_pandas_edge_case(self):
         """Test single price/date being returned as a frame"""
diff --git a/tiingo/api.py b/tiingo/api.py
index f2ec61b..b8b3467 100644
--- a/tiingo/api.py
+++ b/tiingo/api.py
@@ -1,15 +1,22 @@
 # -*- coding: utf-8 -*-
 
-import os
-import sys
-import pkg_resources
+from collections import namedtuple
 import csv
 import json
-from collections import namedtuple
-from zipfile import ZipFile
-from tiingo.restclient import RestClient
-import requests
+import os
 import re
+import sys
+import pkg_resources
+from zipfile import ZipFile
+
+import requests
+
+from tiingo.restclient import RestClient
+from tiingo.exceptions import (
+    InstallPandasException,
+    APIColumnNameError,
+    InvalidFrequencyError,
+    MissingRequiredArgumentError)
 
 try:
     import pandas as pd
@@ -49,17 +56,6 @@ def dict_to_object(item, object_name):
                       object_hook=lambda d:
                       namedtuple(object_name, fields)(*values))
 
-class InstallPandasException(Exception):
-    pass
-
-
-class APIColumnNameError(Exception):
-    pass
-
-
-class InvalidFrequencyError(Exception):
-    pass
-
 
 class TiingoClient(RestClient):
     """Class for managing interactions with the Tiingo REST API
@@ -227,12 +223,16 @@ class TiingoClient(RestClient):
                 frequency (string): Resample frequency (defaults to daily).
         """
 
-        valid_columns = ['open', 'high', 'low', 'close', 'volume', 'adjOpen', 'adjHigh', 'adjLow',
-                         'adjClose', 'adjVolume', 'divCash', 'splitFactor']
+        valid_columns = {'open', 'high', 'low', 'close', 'volume', 'adjOpen', 'adjHigh', 'adjLow',
+                         'adjClose', 'adjVolume', 'divCash', 'splitFactor'}
 
         if metric_name is not None and metric_name not in valid_columns:
             raise APIColumnNameError('Valid data items are: ' + str(valid_columns))
 
+        if metric_name is None and isinstance(tickers, list):
+            raise MissingRequiredArgumentError("""When tickers is provided as a list, metric_name is a required argument.
+            Please provide a metric_name, or call this method with one ticker at a time.""")
+
         params = {
             'format': 'json',
             'resampleFreq': frequency
diff --git a/tiingo/exceptions.py b/tiingo/exceptions.py
new file mode 100644
index 0000000..b510b75
--- /dev/null
+++ b/tiingo/exceptions.py
@@ -0,0 +1,14 @@
+# Exception Clasess
+class InstallPandasException(Exception):
+    pass
+
+
+class APIColumnNameError(Exception):
+    pass
+
+
+class InvalidFrequencyError(Exception):
+    pass
+
+class MissingRequiredArgumentError(Exception):
+    pass