diff --git a/web/src/engine/predictive-text/worker-thread/src/main/correction/search-quotient-root.ts b/web/src/engine/predictive-text/worker-thread/src/main/correction/search-quotient-root.ts
index 845b47c843..8346c62ba1 100644
--- a/web/src/engine/predictive-text/worker-thread/src/main/correction/search-quotient-root.ts
+++ b/web/src/engine/predictive-text/worker-thread/src/main/correction/search-quotient-root.ts
@@ -68,7 +68,7 @@ export class SearchQuotientRoot implements SearchQuotientNode {
    */
   public handleNextNode(): PathResult {
     if(this.hasBeenProcessed) {
-      return null;
+      return { type: 'none' };
     }
 
     this.hasBeenProcessed = true;
diff --git a/web/src/engine/predictive-text/worker-thread/src/main/correction/search-quotient-spur.ts b/web/src/engine/predictive-text/worker-thread/src/main/correction/search-quotient-spur.ts
index ce94280950..fb08e99ce8 100644
--- a/web/src/engine/predictive-text/worker-thread/src/main/correction/search-quotient-spur.ts
+++ b/web/src/engine/predictive-text/worker-thread/src/main/correction/search-quotient-spur.ts
@@ -171,6 +171,10 @@ export abstract class SearchQuotientSpur implements SearchQuotientNode {
   // spaces are in sequence here.
   // `this` = head 'space'.
   public merge(space: SearchQuotientNode): SearchQuotientNode {
+    if(this.model != space.model) {
+      throw new Error("Cannot merge search graphs based on different LexicalModels");
+    }
+
     // Head node for the incoming path is empty, so skip it.
     if(space.parents.length == 0 || space instanceof SearchQuotientRoot) {
       return this;
diff --git a/web/src/test/auto/headless/engine/predictive-text/worker-thread/correction-search/search-quotient-root.tests.ts b/web/src/test/auto/headless/engine/predictive-text/worker-thread/correction-search/search-quotient-root.tests.ts
index a140376c24..f9c15a24ad 100644
--- a/web/src/test/auto/headless/engine/predictive-text/worker-thread/correction-search/search-quotient-root.tests.ts
+++ b/web/src/test/auto/headless/engine/predictive-text/worker-thread/correction-search/search-quotient-root.tests.ts
@@ -23,7 +23,7 @@ import TrieModel = models.TrieModel;
 const testModel = new TrieModel(jsonFixture('models/tries/english-1000'));
 const altModel = new TrieModel(jsonFixture('models/tries/accented'));
 
-describe('SearchQuotientSpur', () => {
+describe('SearchQuotientRoot', () => {
   describe('constructor', () => {
     it('initializes from a lexical model', () => {
       const path = new SearchQuotientRoot(testModel);
@@ -44,7 +44,7 @@ describe('SearchQuotientSpur', () => {
     assert.deepEqual(constituentPaths(path), []);
   });
 
-  describe('.isSameNode returns true for separate instance on same model', () => {
+  it('.isSameNode returns true for separate instance on same model', () => {
     const root1 = new SearchQuotientRoot(testModel);
     const root2 = new SearchQuotientRoot(testModel);