diff --git a/espei/error_functions/zpf_error.py b/espei/error_functions/zpf_error.py
index 422bd872..12e915eb 100644
--- a/espei/error_functions/zpf_error.py
+++ b/espei/error_functions/zpf_error.py
@@ -72,6 +72,8 @@ def _extract_pot_conds(all_conditions: Dict[v.StateVariable, np.ndarray], idx: i
         # Otherwise treat it as a scalar
         if len(cond_val) > 1:
             cond_val = cond_val[idx]
+        else:
+            cond_val = cond_val[0]  # need to explictly extract scalar for NumPy type conversion
         pot_conds[getattr(v, cond_key)] = float(cond_val)
     return pot_conds
 
diff --git a/espei/plot.py b/espei/plot.py
index a00121d4..eba0ff3f 100644
--- a/espei/plot.py
+++ b/espei/plot.py
@@ -391,10 +391,8 @@ def plot_interaction(dbf, comps, phase_name, configuration, output, datasets=Non
             # TODO: Fix this to filter because we need to guarantee the plot points are disordered
             occ = data['solver']['sublattice_occupancies']
             subl_idx = np.nonzero([isinstance(c, (list, tuple)) for c in occ[0]])[0]
-            if len(subl_idx) > 1:
-                subl_idx = int(subl_idx[0])
-            else:
-                subl_idx = int(subl_idx)
+            # Always take the first matching sublattice index
+            subl_idx = int(subl_idx[0])
             indep_var_data = [c[subl_idx][1] for c in occ]
         else:
             interactions = np.array([cond_dict[Symbol('YS')] for cond_dict in sample_condition_dicts])