diff --git a/app/__tests__/builderReducer.test.ts b/app/__tests__/builderReducer.test.ts
index 0a2b53ab..d3a4fbf5 100644
--- a/app/__tests__/builderReducer.test.ts
+++ b/app/__tests__/builderReducer.test.ts
@@ -111,6 +111,15 @@ test('short word warning', () => {
   `);
 });
 
+test('isolated cell warning', () => {
+  const state = getState(['.', '.', '.', '.', 'A', '.', '.', '.', '.'], {});
+  expect(builderReducer(state, publish).publishWarnings).toMatchInlineSnapshot(`
+    [
+      "Some cells are isolated and cannot be clued",
+    ]
+  `);
+});
+
 test('basic enum warnings', () => {
   const state = getState(['a', 'b', 'c', 'g', '', '', 'd', 'e', 'f'], {
     abc: 'test with good enum (3)',
diff --git a/app/reducers/builderReducer.ts b/app/reducers/builderReducer.ts
index 4f23565e..b3f1392c 100644
--- a/app/reducers/builderReducer.ts
+++ b/app/reducers/builderReducer.ts
@@ -1041,6 +1041,9 @@ function _builderReducer(
     if (stats.hasUnches) {
       warnings.push('UNCHES'); // A bit of a hack but PublishWarningsList handles rendering this one
     }
+    if (stats.hasIsolatedCells) {
+      warnings.push('Some cells are isolated and cannot be clued');
+    }
     if (stats.unmatchedRefs.size > 0) {
       warnings.push(
         `Some clues reference entries that don't exist: (${Array.from(
diff --git a/app/reducers/builderUtils.ts b/app/reducers/builderUtils.ts
index 8401139d..ba045a13 100644
--- a/app/reducers/builderUtils.ts
+++ b/app/reducers/builderUtils.ts
@@ -1,6 +1,7 @@
 import { entryWord, hasUnches } from '../lib/gridBase.js';
 import { parseClueEnumeration, parseClueReferences } from '../lib/parse.js';
 import { emptySelection, hasMultipleCells } from '../lib/selection.js';
+import { BLOCK } from '../lib/types.js';
 import { ViewableEntry, entryString } from '../lib/viewableGrid.js';
 import type { BuilderState } from './builderReducer.js';
 import type { GridInterfaceState } from './gridReducer.js';
@@ -128,8 +129,16 @@ export function getWarningStats(state: BuilderState) {
   });
   const enumsExpected = missingEnums.size < numValidClues / 2;
 
+  const hasIsolatedCells = grid.entriesByCell.some(
+    ([across, down], index) =>
+      grid.cells[index] !== BLOCK &&
+      across.entryIndex === null &&
+      down.entryIndex === null
+  );
+
   return {
     shortWords,
+    hasIsolatedCells,
     hasUnches: hasUnches(grid) && !state.userTags.includes('cryptic'),
     unmatchedRefs,
     missingEnums: enumsExpected ? missingEnums : null,