diff --git a/test/test_other.py b/test/test_other.py
index 01e4828d25360..fc2507091312b 100644
--- a/test/test_other.py
+++ b/test/test_other.py
@@ -13547,7 +13547,7 @@ def test_clock_nanosleep(self):
 
   # Tests the internal test suite of tools/unsafe_optimizations.js
   def test_unsafe_optimizations(self):
-    self.run_process(config.NODE_JS_TEST + [path_from_root('tools', 'unsafe_optimizations.js'), '--test'])
+    self.run_process(config.NODE_JS_TEST + [path_from_root('tools', 'unsafe_optimizations.mjs'), '--test'])
 
   @requires_v8
   def test_extended_const(self):
diff --git a/tools/link.py b/tools/link.py
index de7e7972da314..677cba5c9ad1d 100644
--- a/tools/link.py
+++ b/tools/link.py
@@ -2075,7 +2075,7 @@ def phase_final_emitting(options, state, target, wasm_target):
   # optimize by Closure, or unoptimalities that were left behind by processing
   # steps that occurred after Closure.
   if settings.MINIMAL_RUNTIME == 2 and settings.USE_CLOSURE_COMPILER and settings.DEBUG_LEVEL == 0:
-    shared.run_js_tool(utils.path_from_root('tools/unsafe_optimizations.js'), [final_js, '-o', final_js], cwd=utils.path_from_root('.'))
+    shared.run_js_tool(utils.path_from_root('tools/unsafe_optimizations.mjs'), [final_js, '-o', final_js], cwd=utils.path_from_root('.'))
     save_intermediate('unsafe-optimizations')
     # Finally, rerun Closure compile with simple optimizations. It will be able
     # to further minify the code. (n.b. it would not be safe to run in advanced
@@ -2083,7 +2083,7 @@ def phase_final_emitting(options, state, target, wasm_target):
     final_js = building.closure_compiler(final_js, advanced=False, extra_closure_args=options.closure_args)
     # Run unsafe_optimizations.js once more.  This allows the cleanup of newly
     # unused things that closure compiler leaves behind (e.g `new Float64Array(x)`).
-    shared.run_js_tool(utils.path_from_root('tools/unsafe_optimizations.js'), [final_js, '-o', final_js], cwd=utils.path_from_root('.'))
+    shared.run_js_tool(utils.path_from_root('tools/unsafe_optimizations.mjs'), [final_js, '-o', final_js], cwd=utils.path_from_root('.'))
     save_intermediate('unsafe-optimizations2')
 
   fix_es6_import_statements(final_js)
diff --git a/tools/unsafe_optimizations.js b/tools/unsafe_optimizations.mjs
old mode 100644
new mode 100755
similarity index 98%
rename from tools/unsafe_optimizations.js
rename to tools/unsafe_optimizations.mjs
index 67d1d67a2dfa0..f2738a7ffddca
--- a/tools/unsafe_optimizations.js
+++ b/tools/unsafe_optimizations.mjs
@@ -3,11 +3,9 @@
 /** Implements a set of potentially unsafe JavaScript AST optimizations for aggressive code size optimizations.
     Enabled when building with -sMINIMAL_RUNTIME=2 linker flag. */
 
-'use strict';
-
-const acorn = require('acorn');
-const fs = require('fs');
-const terser = require('../third_party/terser/terser');
+import * as fs from 'fs';
+import * as acorn from 'acorn';
+import * as terser from '../third_party/terser/terser.js';
 
 // Starting at the AST node 'root', calls the given callback function 'func' on all children and grandchildren of 'root'
 // that are of any of the type contained in array 'types'.