diff --git a/mitiq/executor/executor.py b/mitiq/executor/executor.py
index 0905da56b..378d6dc8d 100644
--- a/mitiq/executor/executor.py
+++ b/mitiq/executor/executor.py
@@ -41,6 +41,7 @@
     None,  # Untyped executors are assumed to return floats.
     float,
     np.float32,
+    np.float64,
     Iterable[float],
     List[float],
     Sequence[float],