diff --git a/packages/eslint-plugin/src/rules/dot-notation.ts b/packages/eslint-plugin/src/rules/dot-notation.ts
index d0757f55a08..becc2a92727 100644
--- a/packages/eslint-plugin/src/rules/dot-notation.ts
+++ b/packages/eslint-plugin/src/rules/dot-notation.ts
@@ -110,10 +110,9 @@ export default createRule<Options, MessageIds>({
             const objectType = typeChecker.getTypeAtLocation(
               esTreeNodeToTSNodeMap.get(node.object),
             );
-            const indexType = typeChecker.getIndexTypeOfType(
-              objectType,
-              ts.IndexKind.String,
-            );
+            const indexType = objectType
+              .getNonNullableType()
+              .getStringIndexType();
             if (indexType != undefined) {
               return;
             }
diff --git a/packages/eslint-plugin/tests/rules/dot-notation.test.ts b/packages/eslint-plugin/tests/rules/dot-notation.test.ts
index cbdb2d52342..fe25e4de1f1 100644
--- a/packages/eslint-plugin/tests/rules/dot-notation.test.ts
+++ b/packages/eslint-plugin/tests/rules/dot-notation.test.ts
@@ -99,6 +99,25 @@ x['hello'] = 3;
       `,
       options: [{ allowIndexSignaturePropertyAccess: true }],
     },
+    {
+      code: `
+interface Nested {
+  property: string;
+  [key: string]: number | string;
+}
+
+class Dingus {
+  nested: Nested;
+}
+
+let dingus: Dingus | undefined;
+
+dingus?.nested.property;
+dingus?.nested['hello'];
+      `,
+      options: [{ allowIndexSignaturePropertyAccess: true }],
+      parserOptions: { ecmaVersion: 2020 },
+    },
   ],
   invalid: [
     {