diff --git a/tools/uglifyjs.R b/tools/uglifyjs.R
index 2c1796044..33b3b83dc 100644
--- a/tools/uglifyjs.R
+++ b/tools/uglifyjs.R
@@ -2,8 +2,8 @@ uglifyjs = function(file, args = NULL) {
   if (Sys.which('uglifyjs') == '') return(1)
   owd = setwd(dirname(file)); on.exit(setwd(owd), add = TRUE)
   file = basename(file)
-  out = shQuote(xfun::with_ext(file, c('.min.js', '.min.map')))
-  system2('uglifyjs', c(shQuote(file), '-o', out[1], '--source-map', out[2], args))
+  out = shQuote(xfun::with_ext(file, '.min.js'))
+  system2('uglifyjs', c(shQuote(file), '--source-map', '-o', out, args))
 }
 
 xfun::in_dir('inst/resources/gitbook/js', uglifyjs('app.js'))