diff --git a/client/__tests__/util/stateManager/controlsHelpers.test.js b/client/__tests__/util/stateManager/controlsHelpers.test.js
index eed02a14..923d7f5a 100644
--- a/client/__tests__/util/stateManager/controlsHelpers.test.js
+++ b/client/__tests__/util/stateManager/controlsHelpers.test.js
@@ -4,11 +4,21 @@ test controls helpers
 import { subsetAndResetGeneLists } from "../../../src/util/stateManager/controlsHelpers";
 import * as globals from "../../../src/globals";
 
+
 describe("controls helpers", () => {
   test("subsetAndResetGeneLists", () => {
-    const geneList = [...Array(150).keys()].map(
-      () => Math.random().toString(36).substring(2, 6) // random string of 4 characters
-    );
+    const geneList = [];
+    const genRandGene = () => Math.random().toString(36).substring(2, 6);
+
+    // build a unique set of genes
+    for (let i = 0; i < 150; i += 1) {
+      let randGene = genRandGene();
+      while (geneList.includes(randGene)) randGene = genRandGene();
+      geneList.push(randGene);
+    }
+    // insert duplicates
+    geneList[0] = "dupl";
+    geneList[20] = "dupl";
     const state = {
       userDefinedGenes: geneList.slice(0, 20),
       diffexpGenes: geneList.slice(20),
@@ -16,12 +26,14 @@ describe("controls helpers", () => {
     const [newUserDefinedGenes, newDiffExpGenes] = subsetAndResetGeneLists(
       state
     );
+    const expectedNewUserDefinedGenes = [
+      ...geneList.slice(0, 20),
+      ...geneList.slice(21)
+    ].slice(0, globals.maxGenes);
     expect(globals.maxUserDefinedGenes).toBeLessThan(globals.maxGenes);
     expect(geneList.length).toBeGreaterThan(globals.maxGenes);
     expect(newUserDefinedGenes).toHaveLength(globals.maxGenes);
-    expect(newUserDefinedGenes).toStrictEqual(
-      geneList.slice(0, globals.maxGenes)
-    );
+    expect(newUserDefinedGenes).toStrictEqual(expectedNewUserDefinedGenes);
     expect(newDiffExpGenes).toStrictEqual([]);
   });
 });
diff --git a/client/src/util/stateManager/controlsHelpers.js b/client/src/util/stateManager/controlsHelpers.js
index b88ab269..14e22f09 100644
--- a/client/src/util/stateManager/controlsHelpers.js
+++ b/client/src/util/stateManager/controlsHelpers.js
@@ -203,8 +203,7 @@ export function pruneVarDataCache(varData, needed) {
 
 export function subsetAndResetGeneLists(state) {
   const { userDefinedGenes, diffexpGenes } = state;
-  const newUserDefinedGenes = []
-    .concat(userDefinedGenes, diffexpGenes)
+  const newUserDefinedGenes = _.uniq([].concat(userDefinedGenes, diffexpGenes))
     .slice(0, globals.maxGenes);
   const newDiffExpGenes = [];
   return [newUserDefinedGenes, newDiffExpGenes];