diff --git a/conflict_set.py b/conflict_set.py
index 0cc250c..10c68fa 100644
--- a/conflict_set.py
+++ b/conflict_set.py
@@ -58,6 +58,9 @@ _lib.ConflictSet_setOldestVersion.argtypes = (ctypes.c_void_p, ctypes.c_int64)
 
 _lib.ConflictSet_destroy.argtypes = (ctypes.c_void_p,)
 
+_lib.ConflictSet_getBytes.argtypes = (ctypes.c_void_p,)
+_lib.ConflictSet_getBytes.restype = ctypes.c_int64
+
 
 class Result(enum.Enum):
     COMMIT = 0
@@ -106,6 +109,9 @@ class ConflictSet:
     def setOldestVersion(self, version: int) -> None:
         _lib.ConflictSet_setOldestVersion(self.p, version)
 
+    def getBytes(self) -> int:
+        return _lib.ConflictSet_getBytes(self.p)
+
     def __enter__(self):
         return self
 
diff --git a/test_conflict_set.py b/test_conflict_set.py
index 7d45336..ef2aa9e 100644
--- a/test_conflict_set.py
+++ b/test_conflict_set.py
@@ -3,7 +3,10 @@ from conflict_set import *
 
 def test_conflict_set():
     with ConflictSet() as cs:
-        cs.addWrites(1, write(b""))
-        assert cs.check(read(0, b"")) == [Result.CONFLICT]
+        before = cs.getBytes()
+        key = b"a key"
+        cs.addWrites(1, write(key))
+        assert cs.getBytes() - before > 0
+        assert cs.check(read(0, key)) == [Result.CONFLICT]
         cs.setOldestVersion(1)
-        assert cs.check(read(0, b"")) == [Result.TOO_OLD]
+        assert cs.check(read(0, key)) == [Result.TOO_OLD]