diff --git a/src/plots/cartesian/layout_attributes.js b/src/plots/cartesian/layout_attributes.js
index fe77d6fb915..caca53ef82e 100644
--- a/src/plots/cartesian/layout_attributes.js
+++ b/src/plots/cartesian/layout_attributes.js
@@ -329,7 +329,7 @@ module.exports = {
         operation: {
             valType: 'enumerated',
             values: ['[]', '()', '[)', '(]'],
-            dflt: '()',
+            dflt: '[]',
             role: 'info',
             editType: 'calc',
             description: [
diff --git a/test/image/mocks/axes_breaks-finance.json b/test/image/mocks/axes_breaks-finance.json
index 9da3dac8ae1..21b7056a1b6 100644
--- a/test/image/mocks/axes_breaks-finance.json
+++ b/test/image/mocks/axes_breaks-finance.json
@@ -364,11 +364,11 @@
       "rangebreaks": [
         {
           "pattern": "%w",
-          "bounds": [ 6, 0 ],
-          "operation": "[]"
+          "bounds": [ 6, 0 ]
         },
         {
-          "values": ["2017-01-16"]
+          "values": ["2017-01-16"],
+          "operation": "()"
         }
       ]
     },
@@ -377,11 +377,11 @@
       "rangebreaks": [
         {
           "pattern": "%w",
-          "bounds": [ 6, 0 ],
-          "operation": "[]"
+          "bounds": [ 6, 0 ]
         },
         {
-          "values": ["2017-01-16"]
+          "values": ["2017-01-16"],
+          "operation": "()"
         }
       ]
     },
diff --git a/test/image/mocks/axes_breaks-tickvals.json b/test/image/mocks/axes_breaks-tickvals.json
index ddebfa8ed8d..83e7277ad72 100644
--- a/test/image/mocks/axes_breaks-tickvals.json
+++ b/test/image/mocks/axes_breaks-tickvals.json
@@ -20,11 +20,11 @@
         {"bounds": [
           "1969-12-31 23:59:59.999",
           "1970-01-01 00:00:00.090"
-        ]},
+        ], "operation": "()"},
         {"bounds": [
           "1970-01-01 00:00:00.101",
           "1970-01-01 00:00:00.189"
-        ]}
+        ], "operation": "()"}
       ],
       "tickvals": [
         "1969-12-31 23:59:59.980",
diff --git a/test/image/mocks/axes_breaks-values.json b/test/image/mocks/axes_breaks-values.json
index 3469b58471e..a4b7bdbd5fb 100644
--- a/test/image/mocks/axes_breaks-values.json
+++ b/test/image/mocks/axes_breaks-values.json
@@ -14,7 +14,7 @@
   "layout": {
     "xaxis": {
       "rangebreaks": [
-        { "values": [ "2020-01-04", "2020-01-05" ] }
+        { "values": [ "2020-01-04", "2020-01-05" ], "operation": "()" }
       ]
     }
   }
diff --git a/test/jasmine/tests/axes_test.js b/test/jasmine/tests/axes_test.js
index c67109132a9..3f25a078996 100644
--- a/test/jasmine/tests/axes_test.js
+++ b/test/jasmine/tests/axes_test.js
@@ -4179,11 +4179,11 @@ describe('Test axes', function() {
                 }, {
                     xaxis: {
                         rangebreaks: [
-                            {pattern: '%H', bounds: [17, 8]}
+                            {pattern: '%H', bounds: [17, 8], operation: '()'}
                         ]
                     }
                 });
-                _assert('with dflt operation', [
+                _assert('with () operation', [
                     1577952000000, BADNUM,
                     1578038400000, BADNUM,
                     1578124800000, BADNUM,
@@ -4207,7 +4207,7 @@ describe('Test axes', function() {
                 }, {
                     xaxis: {
                         rangebreaks: [
-                            {pattern: '%H', bounds: [17, 8]}
+                            {pattern: '%H', bounds: [17, 8], operation: '()'}
                         ]
                     }
                 });
@@ -4284,7 +4284,7 @@ describe('Test axes', function() {
                             {bounds: [
                                 '1970-01-01 00:00:00.002',
                                 '1970-01-01 00:00:00.003'
-                            ]}
+                            ], operation: '()'}
                         ]
                     }
                 });
@@ -4466,11 +4466,11 @@ describe('Test axes', function() {
                         {bounds: [
                             '1969-12-31 23:59:59.990',
                             '1970-01-01 00:00:00.089'
-                        ]},
+                        ], operation: '()'},
                         {bounds: [
                             '1970-01-01 00:00:00.101',
                             '1970-01-01 00:00:00.189'
-                        ]}
+                        ], operation: '()'}
                     ];
                     return Plotly.react(gd, gd.data, gd.layout);
                 })
@@ -4506,11 +4506,11 @@ describe('Test axes', function() {
                         {bounds: [
                             '1969-12-31 23:59:59.989',
                             '1970-01-01 00:00:00.090'
-                        ]},
+                        ], operation: '()'},
                         {bounds: [
                             '1970-01-01 00:00:00.101',
                             '1970-01-01 00:00:00.300'
-                        ]}
+                        ], operation: '()'}
                     ];
                     return Plotly.react(gd, gd.data, gd.layout);
                 })
@@ -4611,7 +4611,7 @@ describe('Test axes', function() {
                 })
                 .then(function() {
                     gd.layout.xaxis.rangebreaks = [
-                        {pattern: '%w', bounds: [5, 1]}
+                        {pattern: '%w', bounds: [5, 1], operation: '()'}
                     ];
                     return Plotly.react(gd, gd.data, gd.layout);
                 })
@@ -4641,7 +4641,7 @@ describe('Test axes', function() {
                 })
                 .then(function() {
                     gd.layout.xaxis.rangebreaks = [
-                        {pattern: '%w', bounds: [4, 6]}
+                        {pattern: '%w', bounds: [4, 6], operation: '()'}
                     ];
                     return Plotly.react(gd, gd.data, gd.layout);
                 })
@@ -4680,7 +4680,7 @@ describe('Test axes', function() {
                 })
                 .then(function() {
                     gd.layout.xaxis.rangebreaks = [
-                        {pattern: '%H', bounds: [17, 8]}
+                        {pattern: '%H', bounds: [17, 8], operation: '()'}
                     ];
                     return Plotly.react(gd, gd.data, gd.layout);
                 })
@@ -4705,8 +4705,8 @@ describe('Test axes', function() {
                 })
                 .then(function() {
                     gd.layout.xaxis.rangebreaks = [
-                        {pattern: '%w', bounds: [5, 1]},
-                        {pattern: '%H', bounds: [17, 8]}
+                        {pattern: '%w', bounds: [5, 1], operation: '()'},
+                        {pattern: '%H', bounds: [17, 8], operation: '()'}
                     ];
                     return Plotly.react(gd, gd.data, gd.layout);
                 })
@@ -4728,8 +4728,8 @@ describe('Test axes', function() {
                 })
                 .then(function() {
                     gd.layout.xaxis.rangebreaks = [
-                        {pattern: '%H', bounds: [17, 8]},
-                        {pattern: '%w', bounds: [5, 1]}
+                        {pattern: '%H', bounds: [17, 8], operation: '()'},
+                        {pattern: '%w', bounds: [5, 1], operation: '()'}
                     ];
                     return Plotly.react(gd, gd.data, gd.layout);
                 })
@@ -4751,7 +4751,7 @@ describe('Test axes', function() {
                 })
                 .then(function() {
                     gd.layout.xaxis.rangebreaks = [
-                        {pattern: '%H', bounds: [17, 8]}
+                        {pattern: '%H', bounds: [17, 8], operation: '()'}
                     ];
                     // N.B. xaxis.range[0] falls within a break
                     gd.layout.xaxis.autorange = false;
@@ -4772,7 +4772,7 @@ describe('Test axes', function() {
                 })
                 .then(function() {
                     gd.layout.xaxis.rangebreaks = [
-                        {pattern: '%w', bounds: [1, 4]}
+                        {pattern: '%w', bounds: [1, 4], operation: '()'}
                     ];
                     // N.B. xaxis.range[0] falls within a break
                     gd.layout.xaxis.autorange = false;