diff --git a/src/pineko/theory.py b/src/pineko/theory.py
index 0b646c37..4aa2a7cd 100644
--- a/src/pineko/theory.py
+++ b/src/pineko/theory.py
@@ -330,7 +330,7 @@ def eko(self, name, _grid, tcard):
         # from the PTO needed for the PDF evolution (and so by EKO). Here we
         # ensure that the PTO used in the EKO calculation reflects the real
         # perturbative order of the prescription.
-        if "PTOEKO" in tcard:
+        if tcard.get("PTOEKO") is not None:
             tcard["PTO"] = tcard["PTOEKO"]
         # Keys still needed by eko below
         tcard["Qedref"] = tcard["Qref"]