diff --git a/src/stim/circuit/circuit.pybind.cc b/src/stim/circuit/circuit.pybind.cc
index e2e7b9e61..47d3d0181 100644
--- a/src/stim/circuit/circuit.pybind.cc
+++ b/src/stim/circuit/circuit.pybind.cc
@@ -224,7 +224,7 @@ PyPauliString arg_to_pauli_string(const pybind11::object &arg) {
         return PyPauliString(PauliString<MAX_BITWORD_WIDTH>(0));
     } else if (pybind11::isinstance<PyPauliString>(arg)) {
         return pybind11::cast<PyPauliString>(arg);
-    } else if (pybind11::isinstance<std::string>(arg)) {
+    } else if (pybind11::isinstance<pybind11::str>(arg)) {
         return PyPauliString::from_text(pybind11::cast<std::string>(arg).c_str());
     } else {
         throw std::invalid_argument(
diff --git a/src/stim/circuit/circuit_pybind_test.py b/src/stim/circuit/circuit_pybind_test.py
index 0b86ed2af..31fe6510f 100644
--- a/src/stim/circuit/circuit_pybind_test.py
+++ b/src/stim/circuit/circuit_pybind_test.py
@@ -1679,6 +1679,7 @@ def test_has_flow_shorthands():
     assert c.has_flow("_Z -> ZZ", measurements=[0, 2])
     assert c.has_flow("_Z -> ZZ xor rec[0]", measurements=[2])
 
+    assert c.has_flow(start="X_", end="XX", measurements=[1, 3])
     assert not c.has_flow("Z_ -> -Z_")
     assert not c.has_flow("-Z_ -> Z_")
     assert not c.has_flow("Z_ -> X_")