diff --git a/Makefile b/Makefile
index ada925b..5e70dd0 100644
--- a/Makefile
+++ b/Makefile
@@ -33,7 +33,7 @@ BLACK_BIN         = black
 BLACK_OPTS        = --verbose
 
 ROLLUP_BIN        = rollup
-ROLLUP_OPTS       = --config rollup.config.js
+ROLLUP_OPTS       = --config rollup.config.mjs
 
 TRANSCRYPT_BIN    = transcrypt
 TRANSCRYPT_OPTS   = --build --map --nomin --sform --esv 6
diff --git a/README.md b/README.md
index 45c8822..cd3f7dd 100644
--- a/README.md
+++ b/README.md
@@ -60,7 +60,7 @@ Both can be stored locally to use OOMAnalyser without an Internet connection.
 ```
 # . env/bin/activate
 # transcrypt --build --map --nomin -e 6 OOMAnalyser.py
-# rollup --config rollup.config.js
+# rollup --config rollup.config.mjs
 
 or
 
diff --git a/rollup.config.js b/rollup.config.mjs
similarity index 100%
rename from rollup.config.js
rename to rollup.config.mjs