diff --git a/test/functional/api/cas/cache.py b/test/functional/api/cas/cache.py
index 6fd4aa9..f3b08f9 100644
--- a/test/functional/api/cas/cache.py
+++ b/test/functional/api/cas/cache.py
@@ -3,14 +3,14 @@
 # SPDX-License-Identifier: BSD-3-Clause-Clear
 #
 
-from api.cas.cli import *
-from api.cas.casadm_parser import *
-from test_utils.os_utils import *
 from api.cas.cache_config import *
-from storage_devices.device import Device
-from core.test_run import TestRun
 from api.cas.casadm_params import *
+from api.cas.casadm_parser import *
+from api.cas.cli import *
 from api.cas.statistics import CacheStats, IoClassStats
+from core.test_run import TestRun
+from storage_devices.device import Device
+from test_utils.os_utils import *
 
 
 class Cache:
@@ -99,7 +99,7 @@ class Cache:
                                 percentage_val: bool = False):
         stats = get_statistics(self.cache_id, None, io_class_id,
                                stat_filter, percentage_val)
-        return IoClassStats(stats)
+        return IoClassStats(stats, for_cache=True)
 
     def get_statistics(self,
                        stat_filter: List[StatsFilter] = None,
diff --git a/test/functional/api/cas/core.py b/test/functional/api/cas/core.py
index 88a67cc..61fb8ec 100644
--- a/test/functional/api/cas/core.py
+++ b/test/functional/api/cas/core.py
@@ -4,17 +4,16 @@
 #
 
 
-from api.cas.cli import *
-from api.cas.casadm_parser import *
+from datetime import timedelta
+
 from api.cas.cache import Device
+from api.cas.casadm_parser import *
+from api.cas.cli import *
+from api.cas.statistics import CoreStats, IoClassStats
 from test_tools import fs_utils
 from test_utils.os_utils import *
-from api.cas.statistics import CoreStats, IoClassStats
-from datetime import timedelta, datetime
 from test_utils.os_utils import wait
 
-import time
-
 
 class CoreStatus(Enum):
     empty = 0,
@@ -59,7 +58,7 @@ class Core(Device):
                                 percentage_val: bool = False):
         stats = get_statistics(self.cache_id, self.core_id, io_class_id,
                                stat_filter, percentage_val)
-        return IoClassStats(stats)
+        return IoClassStats(stats, for_cache=False)
 
     def get_statistics(self,
                        stat_filter: List[StatsFilter] = None,
diff --git a/test/functional/api/cas/statistics.py b/test/functional/api/cas/statistics.py
index 1e7aa39..ea3ea34 100644
--- a/test/functional/api/cas/statistics.py
+++ b/test/functional/api/cas/statistics.py
@@ -196,7 +196,7 @@ class CoreStats:
 class IoClassStats:
     stats_list = ["config_stats", "usage_stats", "request_stats", "block_stats"]
 
-    def __init__(self, stats):
+    def __init__(self, stats, for_cache: bool):
         try:
             self.config_stats = IoClassConfigStats(
                 stats["io class id"],
@@ -230,16 +230,17 @@ class IoClassStats:
         except KeyError:
             pass
         try:
+            plural = "(s)" if for_cache else ""
             self.block_stats = BlockStats(
-                stats["reads from core(s)"],
-                stats["writes to core(s)"],
-                stats["total to/from core(s)"],
+                stats["reads from core" + plural],
+                stats["writes to core" + plural],
+                stats["total to/from core" + plural],
                 stats["reads from cache"],
                 stats["writes to cache"],
                 stats["total to/from cache"],
-                stats["reads from exported object(s)"],
-                stats["writes to exported object(s)"],
-                stats["total to/from exported object(s)"],
+                stats["reads from exported object" + plural],
+                stats["writes to exported object" + plural],
+                stats["total to/from exported object" + plural],
             )
         except KeyError:
             pass