diff --git a/test/functional/api/cas/casadm.py b/test/functional/api/cas/casadm.py
index 94bca4f45..292cdbad3 100644
--- a/test/functional/api/cas/casadm.py
+++ b/test/functional/api/cas/casadm.py
@@ -380,10 +380,11 @@ def print_statistics(
     filter: List[StatsFilter] = None,
     output_format: OutputFormat = None,
     by_id_path: bool = True,
+    io_class: bool = False,
     shortcut: bool = False,
 ) -> Output:
     _output_format = output_format.name if output_format else None
-    _io_class_id = str(io_class_id) if io_class_id is not None else None
+    _io_class_id = str(io_class_id) if io_class_id is not None else "" if io_class else None
     _core_id = str(core_id) if core_id is not None else None
     if filter is None:
         _filter = filter
diff --git a/test/functional/api/cas/cli.py b/test/functional/api/cas/cli.py
index 3d65aff72..0c8c52e1c 100644
--- a/test/functional/api/cas/cli.py
+++ b/test/functional/api/cas/cli.py
@@ -306,7 +306,7 @@ def print_statistics_cmd(
     command += (" -i " if shortcut else " --cache-id ") + cache_id
     if core_id:
         command += (" -j " if shortcut else " --core-id ") + core_id
-    if io_class_id:
+    if io_class_id is not None:  # might be empty string when printing all io classes
         command += (" -d " if shortcut else " --io-class-id ") + io_class_id
     if filter:
         command += (" -f " if shortcut else " --filter ") + filter