diff --git a/draftlogs/6177_fix.md b/draftlogs/6177_fix.md
new file mode 100644
index 00000000000..8f22a15adb7
--- /dev/null
+++ b/draftlogs/6177_fix.md
@@ -0,0 +1 @@
+ - Fix custom modebar buttons mutate the input [[#6177](https://github.com/plotly/plotly.js/pull/6177)]
\ No newline at end of file
diff --git a/src/components/modebar/manage.js b/src/components/modebar/manage.js
index e75c1c34409..a6e89f9cf2a 100644
--- a/src/components/modebar/manage.js
+++ b/src/components/modebar/manage.js
@@ -8,6 +8,7 @@ var isUnifiedHover = require('../fx/helpers').isUnifiedHover;
 var createModeBar = require('./modebar');
 var modeBarButtons = require('./buttons');
 var DRAW_MODES = require('./constants').DRAW_MODES;
+var extendDeep = require('../../lib').extendDeep;
 
 /**
  * ModeBar wrapper around 'create' and 'update',
@@ -330,7 +331,9 @@ function appendButtonsToGroups(groups, buttons) {
 }
 
 // fill in custom buttons referring to default mode bar buttons
-function fillCustomButton(customButtons) {
+function fillCustomButton(originalModeBarButtons) {
+    var customButtons = extendDeep([], originalModeBarButtons);
+
     for(var i = 0; i < customButtons.length; i++) {
         var buttonGroup = customButtons[i];
 
diff --git a/test/jasmine/tests/modebar_test.js b/test/jasmine/tests/modebar_test.js
index d4f60d1147c..05e310cca48 100644
--- a/test/jasmine/tests/modebar_test.js
+++ b/test/jasmine/tests/modebar_test.js
@@ -996,6 +996,15 @@ describe('ModeBar', function() {
             expect(countButtons(gd._fullLayout._modeBar))
                 .toEqual(initialButtonCount + 6);
         });
+
+        it('sets up buttons without changing the input', function() {
+            var config = [['toImage']];
+            var gd = setupGraphInfo();
+            gd._context.modeBarButtons = config;
+            manageModeBar(gd);
+            expect(config).toEqual([['toImage']]);
+            expect(countButtons(gd._fullLayout._modeBar)).toEqual(2);
+        });
     });
 
     describe('modebar on clicks', function() {