diff --git a/tests/functional/tests/engine/test_io_flags.py b/tests/functional/tests/engine/test_io_flags.py
index d8efbe4..91bddd6 100644
--- a/tests/functional/tests/engine/test_io_flags.py
+++ b/tests/functional/tests/engine/test_io_flags.py
@@ -74,6 +74,8 @@ def test_io_flags(pyocf_ctx, cache_mode):
 
     data = bytes(block_size)
 
+    pyocf_ctx.register_volume_type(FlagsValVolume)
+
     cache_device = FlagsValVolume(Size.from_MiB(50), flags)
     core_device = FlagsValVolume(Size.from_MiB(50), flags)
 
diff --git a/tests/functional/tests/flush/test_flush_after_mngmt.py b/tests/functional/tests/flush/test_flush_after_mngmt.py
index da80983..6719791 100644
--- a/tests/functional/tests/flush/test_flush_after_mngmt.py
+++ b/tests/functional/tests/flush/test_flush_after_mngmt.py
@@ -63,6 +63,8 @@ def test_flush_after_mngmt(pyocf_ctx):
 
     data = bytes(block_size)
 
+    pyocf_ctx.register_volume_type(FlushValVolume)
+
     cache_device = FlushValVolume(Size.from_MiB(50))
     core_device = FlushValVolume(Size.from_MiB(50))