diff --git a/tests/test_tiingo.py b/tests/test_tiingo.py
index bab5587..0d0da23 100644
--- a/tests/test_tiingo.py
+++ b/tests/test_tiingo.py
@@ -6,6 +6,7 @@ from unittest import TestCase
 import vcr
 
 from tiingo import TiingoClient
+from tiingo.api import InvalidFrequencyError
 from tiingo.restclient import RestClientError
 
 
@@ -124,6 +125,13 @@ class TestTickerPrices(TestCase):
         assert len(tickers) > 1
         assert all(ticker['assetType'] == 'ETF' for ticker in tickers)
 
+    def test_invalid_frequency_error(self):
+        with self.assertRaises(InvalidFrequencyError):
+            prices = self._client.get_ticker_price("GOOGL",
+                                                   startDate="2018-01-02",
+                                                   endDate="2018-01-02",
+                                                   frequency="1.5mins")
+
 # tiingo/news
 class TestNews(TestCase):
 
diff --git a/tiingo/api.py b/tiingo/api.py
index c8b7e22..dead54f 100644
--- a/tiingo/api.py
+++ b/tiingo/api.py
@@ -9,6 +9,8 @@ from collections import namedtuple
 from zipfile import ZipFile
 from tiingo.restclient import RestClient
 import requests
+import re
+
 try:
     import pandas as pd
     pandas_is_installed = True
@@ -86,6 +88,8 @@ class TiingoClient(RestClient):
             'User-Agent': 'tiingo-python-client {}'.format(VERSION)
         }
 
+        self._frequency_pattern = re.compile('^[0-9]+(min)$|(hour)$', re.IGNORECASE)
+
     def __repr__(self):
         return '<TiingoClient(url="{}")>'.format(self._base_url)
 
@@ -139,12 +143,8 @@ class TiingoClient(RestClient):
         :return (boolean):
         """
         daily_freqs = ['daily', 'weekly', 'monthly', 'annually']
-        intraday_freqs = ['min', 'hour']
 
-        if frequency.lower() in daily_freqs:
-            return False
-        elif intraday_freqs[0] in frequency.lower() or \
-                intraday_freqs[1] in frequency.lower():
+        if frequency.lower() in daily_freqs or re.match(self._frequency_pattern, frequency):
             return False
         else:
             return True
@@ -159,7 +159,7 @@ class TiingoClient(RestClient):
         if self._invalid_frequency(frequency):
             etext = ("Error: {} is an invalid frequency.  Check Tiingo API documentation "
                      "for valid EOD or intraday frequency format.")
-            raise self.InvalidFrequencyError(etext.format(frequency))
+            raise InvalidFrequencyError(etext.format(frequency))
         else:
             if frequency.lower() in ['daily', 'weekly', 'monthly', 'annually']:
                 return "tiingo/daily/{}/prices"