diff --git a/src/SIL.Machine.Morphology.HermitCrab/MorphologicalRules/AnalysisAffixProcessRule.cs b/src/SIL.Machine.Morphology.HermitCrab/MorphologicalRules/AnalysisAffixProcessRule.cs
index 4e89fef9..89b7f9d3 100644
--- a/src/SIL.Machine.Morphology.HermitCrab/MorphologicalRules/AnalysisAffixProcessRule.cs
+++ b/src/SIL.Machine.Morphology.HermitCrab/MorphologicalRules/AnalysisAffixProcessRule.cs
@@ -56,7 +56,7 @@ public IEnumerable<Word> Apply(Word input)
                 foreach (Word outWord in _rules[i].Apply(input).RemoveDuplicates())
                 {
                     if (!_rule.RequiredSyntacticFeatureStruct.IsEmpty)
-                        outWord.SyntacticFeatureStruct.Add(_rule.RequiredSyntacticFeatureStruct);
+                        outWord.SyntacticFeatureStruct.PriorityUnion(_rule.RequiredSyntacticFeatureStruct);
                     else if (_rule.OutSyntacticFeatureStruct.IsEmpty)
                         outWord.SyntacticFeatureStruct.Clear();
                     outWord.MorphologicalRuleUnapplied(_rule);