diff --git a/pydra/engine/specs.py b/pydra/engine/specs.py
index af152f6f8..a1fc2d6ad 100644
--- a/pydra/engine/specs.py
+++ b/pydra/engine/specs.py
@@ -636,11 +636,12 @@ def _check_requires(self, fld, inputs):
 
         if "requires" in fld.metadata:
             # if requires is a list of list it is treated as el[0] OR el[1] OR...
-            if all([isinstance(el, list) for el in fld.metadata["requires"]]):
-                field_required_OR = fld.metadata["requires"]
+            required_fields = ensure_list(fld.metadata["requires"])
+            if all([isinstance(el, list) for el in required_fields]):
+                field_required_OR = required_fields
             # if requires is a list of tuples/strings - I'm creating a 1-el nested list
-            elif all([isinstance(el, (str, tuple)) for el in fld.metadata["requires"]]):
-                field_required_OR = [fld.metadata["requires"]]
+            elif all([isinstance(el, (str, tuple)) for el in required_fields]):
+                field_required_OR = [required_fields]
             else:
                 raise Exception(
                     f"requires field can be a list of list, or a list "