diff --git a/findatapy/market/marketdatagenerator.py b/findatapy/market/marketdatagenerator.py
index 7be5c3a..c68798b 100644
--- a/findatapy/market/marketdatagenerator.py
+++ b/findatapy/market/marketdatagenerator.py
@@ -319,6 +319,10 @@ def fetch_group_time_series(self, market_data_request_list):
             thread_no = DataConstants().market_thread_no[market_data_request_list[0].data_source]
 
         if thread_no > 0:
+            # limit the threads to the number of available CPUs
+            from multiprocessing import cpu_count
+            thread_no = min(cpu_count(),thread_no)
+            
             pool = Pool(thread_no)
 
             # open the market data downloads in their own threads and return the results
@@ -417,4 +421,4 @@ def create_category_key(self, market_data_request, ticker=None):
         return key
 
     def create_cache_file_name(self, filename):
-        return DataConstants().folder_time_series_data + "/" + filename
\ No newline at end of file
+        return DataConstants().folder_time_series_data + "/" + filename