diff --git a/qualtran/bloqs/qft/two_bit_ffft.py b/qualtran/bloqs/qft/two_bit_ffft.py
index eadb983db..26b7bf889 100644
--- a/qualtran/bloqs/qft/two_bit_ffft.py
+++ b/qualtran/bloqs/qft/two_bit_ffft.py
@@ -12,9 +12,10 @@
 #  See the License for the specific language governing permissions and
 #  limitations under the License.
 from functools import cached_property
-from typing import Any, Dict, Set, TYPE_CHECKING
+from typing import Any, Dict, Set, TYPE_CHECKING, Union
 
 import numpy as np
+import sympy
 from attrs import frozen
 from numpy.typing import NDArray
 
@@ -73,7 +74,7 @@ class TwoBitFFFT(Bloq):
 
     k: int
     n: int
-    eps: float = 1e-10
+    eps: Union[float, sympy.Expr] = 1e-10
     is_adjoint: bool = False
 
     def __attrs_post_init__(self):