diff --git a/src/plot_api/plot_api.js b/src/plot_api/plot_api.js
index a6875712fd5..6b00272b00a 100644
--- a/src/plot_api/plot_api.js
+++ b/src/plot_api/plot_api.js
@@ -1922,8 +1922,24 @@ function _relayout(gd, aobj) {
         // back to its initial value as computed during the first pass in Plots.plotAutoSize.
         //
         // To do so, we must manually set them back here using the _initialAutoSize cache.
-        if(['width', 'height'].indexOf(ai) !== -1 && vi === null) {
-            fullLayout[ai] = gd._initialAutoSize[ai];
+        // can't use impliedEdits for this because behavior depends on vi
+        if(['width', 'height'].indexOf(ai) !== -1) {
+            if(vi) {
+                doextra('autosize', null);
+                // currently we don't support autosize one dim only - so
+                // explicitly set the other one. Note that doextra will
+                // ignore this if the same relayout call also provides oppositeAttr
+                var oppositeAttr = ai === 'height' ? 'width' : 'height';
+                doextra(oppositeAttr, fullLayout[oppositeAttr]);
+            }
+            else {
+                fullLayout[ai] = gd._initialAutoSize[ai];
+            }
+        }
+        else if(ai === 'autosize') {
+            // depends on vi here too, so again can't use impliedEdits
+            doextra('width', vi ? null : fullLayout.width);
+            doextra('height', vi ? null : fullLayout.height);
         }
         // check autorange vs range
         else if(pleafPlus.match(AX_RANGE_RE)) {
diff --git a/test/jasmine/tests/config_test.js b/test/jasmine/tests/config_test.js
index e85451e6a5d..395b8f36d4e 100644
--- a/test/jasmine/tests/config_test.js
+++ b/test/jasmine/tests/config_test.js
@@ -47,7 +47,12 @@ describe('config argument', function() {
                 width: layoutWidth
             };
             var relayout = {
-                width: relayoutWidth
+                width: relayoutWidth,
+                // didn't need this before #3120 - but since we're now
+                // implicitly clearing autosize when edit width, if you really
+                // want height to re-autosize you need to explicitly re-add
+                // autosize
+                autosize: autosize
             };
 
             var layout2 = Lib.extendDeep({}, layout);
diff --git a/test/jasmine/tests/plot_api_test.js b/test/jasmine/tests/plot_api_test.js
index e5ab15363ed..3ff769c6ece 100644
--- a/test/jasmine/tests/plot_api_test.js
+++ b/test/jasmine/tests/plot_api_test.js
@@ -510,6 +510,43 @@ describe('Test plot api', function() {
             .catch(failTest)
             .then(done);
         });
+
+        it('updates autosize/width/height correctly', function(done) {
+            function assertSizeAndThen(width, height, auto, msg, next) {
+                return function() {
+                    expect(gd._fullLayout.width).toBe(width, msg);
+                    expect(gd._fullLayout.height).toBe(height, msg);
+                    expect(gd._fullLayout.autosize).toBe(auto, msg);
+                    if(!auto) {
+                        expect(gd.layout.width).toBe(width, msg);
+                        expect(gd.layout.height).toBe(height, msg);
+                    }
+
+                    if(next) return Plotly.relayout(gd, next);
+                };
+            }
+
+            // give gd css sizing to be picked up by autosize
+            gd.style.width = '543px';
+            gd.style.height = '432px';
+
+            Plotly.newPlot(gd, [{y: [1, 3, 2]}])
+            .then(assertSizeAndThen(543, 432, true, 'initial',
+                {autosize: false}))
+            .then(assertSizeAndThen(543, 432, false, 'autosize false with no sizes',
+                {autosize: true}))
+            .then(assertSizeAndThen(543, 432, true, 'back to autosized',
+                {width: 600}))
+            .then(assertSizeAndThen(600, 432, false, 'explicit width causes explicit height',
+                {width: null}))
+            .then(assertSizeAndThen(543, 432, true, 'removed width',
+                {height: 500, width: 700}))
+            .then(assertSizeAndThen(700, 500, false, 'explicit height and width',
+                {autosize: true}))
+            .then(assertSizeAndThen(543, 432, true, 'final back to autosize'))
+            .catch(failTest)
+            .then(done);
+        });
     });
 
     describe('Plotly.relayout subroutines switchboard', function() {