diff --git a/trezorlib/tx_api.py b/trezorlib/tx_api.py
index 6a787b823..b1dd2b5de 100644
--- a/trezorlib/tx_api.py
+++ b/trezorlib/tx_api.py
@@ -45,9 +45,9 @@ class TxApi(object):
             j = r.json()
         except:
             raise Exception('URL error: %s' % url)
-        if cache_file:
+        if cache_dir and cache_file:
             try: # saving into cache
-                json.dump(j, open(cachefile, 'w'))
+                json.dump(j, open(cache_file, 'w'))
             except:
                 pass
         return j