diff --git a/test/test_except.py b/test/test_except.py
index 1e9c0045..57bc4280 100644
--- a/test/test_except.py
+++ b/test/test_except.py
@@ -4,7 +4,7 @@
 import gc
 import tracemalloc
 
-from pytest import raises
+from pytest import mark, raises
 
 from msgpack import ExtType, FormatError, OutOfData, StackError, Unpacker, packb, unpackb
 
@@ -103,6 +103,7 @@ def test_invalidvalue():
         unpacker.skip()
 
 
+@mark.thread_unsafe(reason="tracemalloc changes process-wide state and measures all threads")
 def test_no_memory_leak_on_nested_invalid_tag() -> None:
     """Regression test: unpacking nested arrays containing an invalid tag must not leak objects."""
 
diff --git a/test/test_limits.py b/test/test_limits.py
index ae6503da..6ba73ce3 100644
--- a/test/test_limits.py
+++ b/test/test_limits.py
@@ -153,6 +153,7 @@ def test_pairs_preallocation_boundary(size):
 
 
 @pytest.mark.parametrize("kind", ["list", "tuple", "pairs"])
+@pytest.mark.thread_unsafe(reason="tracemalloc changes process-wide state and measures all threads")
 def test_nested_headers_preallocation(kind):
     packer = Packer()
     header = (