diff --git a/src/traces/heatmap/plot.js b/src/traces/heatmap/plot.js
index 3162c86069e..a4f7ac2c0e7 100644
--- a/src/traces/heatmap/plot.js
+++ b/src/traces/heatmap/plot.js
@@ -323,7 +323,7 @@ function plotOne(gd, plotinfo, cd) {
             for(j = 0; j < m; j++) {
                 row = z[j];
                 yb = ypx(j);
-                for(i = 0; i < n; i++) {
+                for(i = 0; i < imageWidth; i++) {
                     c = setColor(row[i], 1);
                     pxIndex = (yb * imageWidth + xpx(i)) * 4;
                     putColor(pixels, pxIndex, c);
diff --git a/test/image/baselines/Earth_heatmap.png b/test/image/baselines/Earth_heatmap.png
index d5776d6dffd..bb1397cdbce 100644
Binary files a/test/image/baselines/Earth_heatmap.png and b/test/image/baselines/Earth_heatmap.png differ
diff --git a/test/image/baselines/zsmooth_methods.png b/test/image/baselines/zsmooth_methods.png
new file mode 100644
index 00000000000..4fcbf75279e
Binary files /dev/null and b/test/image/baselines/zsmooth_methods.png differ
diff --git a/test/image/mocks/Earth_heatmap.json b/test/image/mocks/Earth_heatmap.json
index e94513e68dd..8c82e8e575e 100644
--- a/test/image/mocks/Earth_heatmap.json
+++ b/test/image/mocks/Earth_heatmap.json
@@ -2604,7 +2604,8 @@
         ]
       ],
       "scl": "Earth",
-      "type": "heatmap"
+      "type": "heatmap",
+      "zsmooth": "fast"
     }
   ],
   "layout": {
diff --git a/test/image/mocks/zsmooth_methods.json b/test/image/mocks/zsmooth_methods.json
new file mode 100644
index 00000000000..5916d51b57a
--- /dev/null
+++ b/test/image/mocks/zsmooth_methods.json
@@ -0,0 +1,129 @@
+{
+    "data": [
+        {
+            "z": [
+                [
+                    0.1189977,
+                    0.3403857,
+                    0.7512671,
+                    0.6990767,
+                    0.5472155
+                ],
+                [
+                    0.4983641,
+                    0.5852678,
+                    0.2550951,
+                    0.8909033,
+                    0.1386244
+                ],
+                [
+                    0.959744,
+                    0.2238119,
+                    0.5059571,
+                    0.9592914,
+                    0.149294
+                ]
+            ],
+            "scl": "Jet",
+            "zsmooth": "best",
+            "type": "heatmap",
+            "xaxis": "x",
+            "yaxis": "y"
+        },
+        {
+            "z": [
+                [
+                    0.1189977,
+                    0.3403857,
+                    0.7512671,
+                    0.6990767,
+                    0.5472155
+                ],
+                [
+                    0.4983641,
+                    0.5852678,
+                    0.2550951,
+                    0.8909033,
+                    0.1386244
+                ],
+                [
+                    0.959744,
+                    0.2238119,
+                    0.5059571,
+                    0.9592914,
+                    0.149294
+                ]
+            ],
+            "scl": "Jet",
+            "zsmooth": "fast",
+            "type": "heatmap",
+            "xaxis": "x2",
+            "yaxis": "y2"
+        },
+        {
+            "z": [
+                [
+                    0.1189977,
+                    0.3403857,
+                    0.7512671,
+                    0.6990767,
+                    0.5472155
+                ],
+                [
+                    0.4983641,
+                    0.5852678,
+                    0.2550951,
+                    0.8909033,
+                    0.1386244
+                ],
+                [
+                    0.959744,
+                    0.2238119,
+                    0.5059571,
+                    0.9592914,
+                    0.149294
+                ]
+            ],
+            "scl": "Jet",
+            "zsmooth": false,
+            "type": "heatmap",
+            "xaxis": "x3",
+            "yaxis": "y3"
+        }
+    ],
+    "layout": {
+        "title": "zsmooth: best, fast, false",
+        "width": 800,
+        "height": 350,
+        "xaxis": {
+          "domain": [
+            0,
+            0.31
+          ],
+          "anchor": "y"
+        },
+        "yaxis": {
+          "anchor": "x"
+        },
+        "xaxis2": {
+          "domain": [
+            0.35,
+            0.64
+          ],
+          "anchor": "y2"
+        },
+        "yaxis2": {
+          "anchor": "x2"
+        },
+        "xaxis3": {
+          "domain": [
+            0.68,
+            1
+          ],
+          "anchor": "y3"
+        },
+        "yaxis3": {
+          "anchor": "x3"
+        }
+    }
+}