diff --git a/src/plots/cartesian/axis_autotype.js b/src/plots/cartesian/axis_autotype.js
index e5a399784b3..c7b90565985 100644
--- a/src/plots/cartesian/axis_autotype.js
+++ b/src/plots/cartesian/axis_autotype.js
@@ -38,15 +38,20 @@ function linearOK(array) {
 // 2- or 4-digit integers can be both, so require twice as many
 // dates as non-dates, to exclude cases with mostly 2 & 4 digit
 // numbers and a few dates
+// as with categories, consider DISTINCT values only.
 function moreDates(a, calendar) {
-    var dcnt = 0,
-        ncnt = 0,
-        // test at most 1000 points, evenly spaced
-        inc = Math.max(1, (a.length - 1) / 1000),
-        ai;
+    // test at most 1000 points, evenly spaced
+    var inc = Math.max(1, (a.length - 1) / 1000);
+    var dcnt = 0;
+    var ncnt = 0;
+    var seen = {};
 
     for(var i = 0; i < a.length; i += inc) {
-        ai = a[Math.round(i)];
+        var ai = a[Math.round(i)];
+        var stri = String(ai);
+        if(seen[stri]) continue;
+        seen[stri] = 1;
+
         if(Lib.isDateTime(ai, calendar)) dcnt += 1;
         if(isNumeric(ai)) ncnt += 1;
     }
@@ -55,18 +60,23 @@ function moreDates(a, calendar) {
 }
 
 // are the (x,y)-values in gd.data mostly text?
-// require twice as many categories as numbers
+// require twice as many DISTINCT categories as distinct numbers
 function category(a) {
     // test at most 1000 points
-    var inc = Math.max(1, (a.length - 1) / 1000),
-        curvenums = 0,
-        curvecats = 0,
-        ai;
+    var inc = Math.max(1, (a.length - 1) / 1000);
+    var curvenums = 0;
+    var curvecats = 0;
+    var seen = {};
 
     for(var i = 0; i < a.length; i += inc) {
-        ai = a[Math.round(i)];
-        if(Lib.cleanNumber(ai) !== BADNUM) curvenums++;
-        else if(typeof ai === 'string' && ai !== '' && ai !== 'None') curvecats++;
+        var ai = a[Math.round(i)];
+        var stri = String(ai);
+        if(seen[stri]) continue;
+        seen[stri] = 1;
+
+        if(typeof ai === 'boolean') curvecats++;
+        else if(Lib.cleanNumber(ai) !== BADNUM) curvenums++;
+        else if(typeof ai === 'string') curvecats++;
     }
 
     return curvecats > curvenums * 2;
diff --git a/test/jasmine/tests/axes_test.js b/test/jasmine/tests/axes_test.js
index bfc15effcc0..4962bd75908 100644
--- a/test/jasmine/tests/axes_test.js
+++ b/test/jasmine/tests/axes_test.js
@@ -189,6 +189,80 @@ describe('Test axes', function() {
             fullData = [];
         });
 
+        describe('autotype', function() {
+            function supplyWithTrace(trace) {
+                var fullTrace = Lib.extendDeep(
+                    {type: 'scatter', xaxis: 'x', yaxis: 'y'},
+                    trace
+                );
+                layoutIn = {xaxis: {}, yaxis: {}};
+                supplyLayoutDefaults(layoutIn, layoutOut, [fullTrace]);
+            }
+
+            function checkTypes(xType, yType, msg) {
+                expect(layoutOut.xaxis.type).toBe(xType, msg);
+                expect(layoutOut.yaxis.type).toBe(yType, msg);
+            }
+
+            it('treats booleans as categories', function() {
+                supplyWithTrace({x: [0, 1, 2], y: [true, false, true]});
+                checkTypes('linear', 'category');
+            });
+
+            it('sees a single "None" or "" as a category', function() {
+                supplyWithTrace({x: ['None'], y: ['']});
+                checkTypes('category', 'category');
+            });
+
+            it('lets a single number beat up to two distinct categories', function() {
+                supplyWithTrace({
+                    x: ['2.1', 'N/A', '', 'N/A', '', 'N/A', 'N/A', '', '', ''],
+                    y: [0, 'None', true, 'None', 'None', 'None', 'None', 'None']
+                });
+                checkTypes('linear', 'linear');
+            });
+
+            it('turns back to category with >2 per distinct number', function() {
+                supplyWithTrace({
+                    x: [4, 4, 4, 4, 4, 4, 4, 4, 'Yes', 'No', 'Maybe'],
+                    y: [1, 2, 1, 2, 1, 2, true, false, '', 'None', 'nan']
+                });
+                checkTypes('category', 'category');
+            });
+
+            it('works with world calendars', function() {
+                // these are only valid dates in chinese
+                var intercalary = ['1995-08i-01', '1995-08i-29', '1984-10i-15'];
+                supplyWithTrace({
+                    x: intercalary, xcalendar: 'chinese',
+                    y: intercalary, ycalendar: 'gregorian'
+                });
+                checkTypes('date', 'category');
+            });
+
+            it('requires >twice as many distinct dates as numbers', function() {
+                supplyWithTrace({
+                    x: ['2000-01-01', '2000-01-02', '2000-01-03', 1, 1.2],
+                    y: ['2000-01', '2000-02', '2000-03', '2000-04', 1.1]
+                });
+                checkTypes('linear', 'date');
+
+                supplyWithTrace({
+                    x: ['2000-01-01', '2000-01-02', '2000-01-03', 1, 1],
+                    y: ['2000-01', '2000-01', '2000-01', '2000-01', 1.1]
+                });
+                checkTypes('date', 'linear');
+            });
+
+            it('counts ambiguous dates as both dates and numbers', function() {
+                supplyWithTrace({
+                    x: ['2000', '2000-01', '2000-02'], // 3 dates, 1 number
+                    y: ['2000', '2001', '2000-01'] // 3 dates, 2 numbers
+                });
+                checkTypes('date', 'linear');
+            });
+        });
+
         it('should set undefined linewidth/linecolor if linewidth, linecolor or showline is not supplied', function() {
             layoutIn = {
                 xaxis: {},