diff --git a/src/mol-model-props/computed/membrane-orientation/ANVIL.ts b/src/mol-model-props/computed/membrane-orientation/ANVIL.ts
index b40e5dccf239c448f0e0cf11c7c9070e5fd87f29..23f1d0d8230a6b5032447442c427fcee2a57eab1 100644
--- a/src/mol-model-props/computed/membrane-orientation/ANVIL.ts
+++ b/src/mol-model-props/computed/membrane-orientation/ANVIL.ts
@@ -336,9 +336,9 @@ namespace HphobHphil {
     }
 
     // ANVIL-specific (not general) definition of membrane-favoring amino acids
-    const HYDROPHOBIC_AMINO_ACIDS = ['ALA', 'CYS', 'GLY', 'HIS', 'ILE', 'LEU', 'MET', 'PHE', 'SER', 'THR', 'VAL'];
+    const HYDROPHOBIC_AMINO_ACIDS = new Set(['ALA', 'CYS', 'GLY', 'HIS', 'ILE', 'LEU', 'MET', 'PHE', 'SER', 'THR', 'VAL']);
     function isHydrophobic(label_comp_id: string): boolean {
-        return HYDROPHOBIC_AMINO_ACIDS.indexOf(label_comp_id) !== -1;
+        return HYDROPHOBIC_AMINO_ACIDS.has(label_comp_id);
     }
 }