diff --git a/src/pineko/evolve.py b/src/pineko/evolve.py
index b40c6cc3..39f65e6a 100644
--- a/src/pineko/evolve.py
+++ b/src/pineko/evolve.py
@@ -173,7 +173,10 @@ def write_operator_card(pineappl_grid, default_card, card_path, tcard):
             opconf["ev_op_iterations"] = 1
         elif tcard["ModEv"] == "EXA":
             opconf["evolution_method"] = "iterate-exact"
-            opconf["ev_op_iterations"] = tcard["IterEv"]
+            if "IterEv" in tcard:
+                opconf["ev_op_iterations"] = tcard["IterEv"]
+            elif "IterEv" not in default_card["configs"]:
+                raise ValueError("IterEv not found in both the theory and the template")
 
         # If the information was also in the template _and it is different_, warn
         for key in ["evolution_method", "ev_op_iterations"]:
diff --git a/tests/test_evolve.py b/tests/test_evolve.py
index 51621062..1815654d 100644
--- a/tests/test_evolve.py
+++ b/tests/test_evolve.py
@@ -50,22 +50,22 @@ def test_write_operator_card_q0(tmp_path):
     """Checks https://github.com/NNPDF/pineko/issues/146"""
     p = tmp_path / "q0.yaml"
     g = FakePine()
-    # 1. defaults
     t = copy.deepcopy(default_card)
     o = copy.deepcopy(example.raw_operator())
+    # 1. Same Q0 and mu0, all ok
+    t["Q0"] = 5.0
+    o["mu0"] = 5.0
     _xs, _mu2s = pineko.evolve.write_operator_card(g, o, p, t)
     with open(p, encoding="utf8") as f:
         oo = yaml.safe_load(f)
     np.testing.assert_allclose(oo["mu0"], t["Q0"])
-    # 2. overwriting from theory side
-    t["Q0"] = 10.0
+    # 2. Q0 only in theory, all ok
+    o.pop("mu0")
     _xs, _mu2s = pineko.evolve.write_operator_card(g, o, p, t)
     with open(p, encoding="utf8") as f:
         oo = yaml.safe_load(f)
     np.testing.assert_allclose(oo["mu0"], t["Q0"])
-    # 3. op template is ignored
+    # 3. op is different, raises error
     o["mu0"] = 11.0
-    _xs, _mu2s = pineko.evolve.write_operator_card(g, o, p, t)
-    with open(p, encoding="utf8") as f:
-        oo = yaml.safe_load(f)
-    np.testing.assert_allclose(oo["mu0"], t["Q0"])
+    with pytest.raises(ValueError):
+        _xs, _mu2s = pineko.evolve.write_operator_card(g, o, p, t)