diff --git a/js/main-editor.js b/js/main-editor.js
index e989d81..344d678 100644
--- a/js/main-editor.js
+++ b/js/main-editor.js
@@ -1,4 +1,4 @@
-import * as fflate from './vendor/fflate.mjs';
+import * as fflate from './vendor/fflate.js';
 
 import { DIRECTIONS, LAYERS, TICS_PER_SECOND } from './defs.js';
 import { TILES_WITH_PROPS } from './editor-tile-overlays.js';
diff --git a/js/main.js b/js/main.js
index ebbe86c..196b623 100644
--- a/js/main.js
+++ b/js/main.js
@@ -1,6 +1,6 @@
 // TODO bugs and quirks i'm aware of:
 // - steam: if a player character starts on a force floor they won't be able to make any voluntary movements until they are no longer on a force floor
-import * as fflate from './vendor/fflate.mjs';
+import * as fflate from './vendor/fflate.js';
 
 import { COMPAT_FLAGS, COMPAT_RULESET_LABELS, COMPAT_RULESET_ORDER, DIRECTIONS, INPUT_BITS, TICS_PER_SECOND, compat_flags_for_ruleset } from './defs.js';
 import * as c2g from './format-c2g.js';
diff --git a/js/util.js b/js/util.js
index 02bc957..8122e88 100644
--- a/js/util.js
+++ b/js/util.js
@@ -1,4 +1,4 @@
-import * as fflate from './vendor/fflate.mjs';
+import * as fflate from './vendor/fflate.js';
 
 // Base class for custom errors
 export class LLError extends Error {}
diff --git a/js/vendor/fflate.mjs b/js/vendor/fflate.js
similarity index 100%
rename from js/vendor/fflate.mjs
rename to js/vendor/fflate.js