diff --git a/src/rules/extensions.ts b/src/rules/extensions.ts
index 7f8c5f82..37bee6a5 100644
--- a/src/rules/extensions.ts
+++ b/src/rules/extensions.ts
@@ -370,10 +370,13 @@ export default createRule<Options, MessageId>({
             })
             const fixOrSuggest = {
               fix(fixer: TSESLint.RuleFixer) {
-                return fixer.replaceText(
-                  source,
-                  replaceImportPath(source.raw, fixedImportPath),
+                const newImportPath = replaceImportPath(
+                  source.raw,
+                  fixedImportPath,
                 )
+                return source.raw === newImportPath
+                  ? null // Surface that something has gone wrong with extension detection.
+                  : fixer.replaceText(source, newImportPath)
               },
             }
             context.report({
diff --git a/test/rules/extensions.spec.ts b/test/rules/extensions.spec.ts
index f7824036..f75fa395 100644
--- a/test/rules/extensions.spec.ts
+++ b/test/rules/extensions.spec.ts
@@ -250,6 +250,18 @@ ruleTester.run('extensions', rule, {
       ],
       output: null,
     }),
+    tInvalid({
+      name: 'extensions should not autofix when the fix is identical',
+      code: 'import foo from "./unresolved"',
+      options: ['always', { fix: true }],
+      errors: [
+        {
+          messageId: 'missing',
+          data: { extension: 'js', importPath: './unresolved' },
+        },
+      ],
+      output: null,
+    }),
     tInvalid({
       code: 'import a from "a/index.js"',
       errors: [