diff --git a/src/sao.js b/src/sao.js
index d63a8420e6..3d26e9a7fb 100644
--- a/src/sao.js
+++ b/src/sao.js
@@ -168,6 +168,27 @@ var Sao = {};
 
     Sao.Decimal = Number;
 
+    var _moment_to_string = moment.prototype.toString;
+    moment.prototype.toString = function() {
+        if (this.isDate) {
+            return this.format('YYYY-MM-DD');
+        } else if (this.isDateTime) {
+            if (this.milliseconds()) {
+                return this.format('YYYY-MM-DD HH:mm:ss.SSSSSS');
+            } else {
+                return this.format('YYYY-MM-DD HH:mm:ss');
+            }
+        } else if (this.isTime) {
+            if (this.milliseconds()) {
+                return this.format('HH:mm:ss.SSSSSS');
+            } else {
+                return this.format('HH:mm:ss');
+            }
+        } else {
+            return _moment_to_string.call(this);
+        }
+    };
+
     Sao.Date = function(year, month, day, utc) {
         var date;
         if (month === undefined) {
@@ -185,9 +206,6 @@ var Sao = {};
         date.date(day);
         date.set({hour: 0, minute: 0, second: 0, millisecond: 0});
         date.isDate = true;
-        date.toString = function() {
-            return this.format('YYYY-MM-DD');
-        };
         return date;
     };
 
@@ -234,13 +252,6 @@ var Sao = {};
             datetime.milliseconds(millisecond);
         }
         datetime.isDateTime = true;
-        datetime.toString = function() {
-            if (this.milliseconds()) {
-                return this.format('YYYY-MM-DD HH:mm:ss.SSSSSS');
-            } else {
-                return this.format('YYYY-MM-DD HH:mm:ss');
-            }
-        };
         datetime.local();
         return datetime;
     };
diff --git a/src/view/graph.js b/src/view/graph.js
index e388c6cb09..7427cdf1b6 100644
--- a/src/view/graph.js
+++ b/src/view/graph.js
@@ -98,7 +98,7 @@
                     var x = record.field_get_client(this.xfield.name);
                     // c3 does not support moment
                     if (x && (x.isDate || x.isDateTime)) {
-                        x = x.toDate();
+                        x = x.toString();
                     }
                     data.columns[0][index + 1] = x;
                     this._add_id(x, record.id);
@@ -177,18 +177,21 @@
             c3_config.data.x = 'labels';
             c3_config.data.onclick = this.action.bind(this);
 
-            var type = this.xfield.type;
+            var type = this.view.screen.model.fields[this.xfield.name]
+                .description.type;
             if ((type == 'date') || (type == 'datetime')) {
                 var format_func, date_format, time_format;
                 date_format = Sao.common.date_format(
                     this.view.screen.context.date_format);
                 time_format = '%X';
                 if (type == 'datetime') {
+                    c3_config.data.xFormat = '%Y-%m-%d %H:%M:%S';
                     format_func = function(dt) {
                         return Sao.common.format_datetime(date_format,
                                 time_format, moment(dt));
                     };
                 } else {
+                    c3_config.data.xFormat = '%Y-%m-%d';
                     format_func = function(dt) {
                         return Sao.common.format_date(date_format, moment(dt));
                     };
@@ -286,7 +289,8 @@
             delete config.axis;
             delete config.data.x;
             var format_func;
-            var type = this.xfield.type;
+            var type = this.view.screen.model.fields[this.xfield.name]
+                .description.type;
             if ((type == 'date') || (type == 'datetime')) {
                 var date_format = Sao.common.date_format(
                     this.view.screen.context.date_format);
diff --git a/tests/sao.js b/tests/sao.js
index 1806554ac6..c62f8b1c76 100644
--- a/tests/sao.js
+++ b/tests/sao.js
@@ -2918,6 +2918,27 @@
             ["Active: False", "Active: True"]));
     });
 
+    QUnit.test('Date.toString', function() {
+        QUnit.strictEqual(Sao.Date(2020, 8, 11).toString(), '2020-09-11');
+    });
+
+    QUnit.test('DateTime.toString', function() {
+        QUnit.strictEqual(
+            Sao.DateTime(2020, 8, 11, 10, 30, 42).toString(),
+            '2020-09-11 10:30:42');
+
+        QUnit.strictEqual(
+            Sao.DateTime(2020, 8, 11, 10, 30, 42, 123).toString(),
+            '2020-09-11 10:30:42.123000');
+    });
+
+    QUnit.test('Time.toString', function() {
+        QUnit.strictEqual(Sao.Time(10, 30, 42).toString(), '10:30:42');
+
+        QUnit.strictEqual(
+            Sao.Time(10, 30, 42, 123).toString(), '10:30:42.123000');
+    });
+
     QUnit.test('HTML Sanitization', function() {
         var examples = [
             ["Test", "Test"],