diff --git a/lib/rules/unit-no-unknown/README.md b/lib/rules/unit-no-unknown/README.md
index 2d41213bab..3d11d5ddff 100644
--- a/lib/rules/unit-no-unknown/README.md
+++ b/lib/rules/unit-no-unknown/README.md
@@ -33,19 +33,19 @@ The following patterns are *not* considered violations:
 ```css
 a {
   width: 10px;
-}  
+}
 ```
 
 ```css
 a {
   width: 10Px;
-}  
+}
 ```
 
 ```css
 a {
   width: 10pX;
-}  
+}
 ```
 
 ```css
@@ -83,3 +83,43 @@ a {
   width: 10my-other-unit;
 }
 ```
+
+### `ignoreFunctions: ["/regex/", "string"]`
+
+Given:
+
+```js
+["image-set", "/^my-/", "/^YOUR-/i"]
+```
+
+The following patterns are *not* considered violations:
+
+```css
+a {
+  background-image: image-set(
+    '/images/some-image-1x.jpg' 1x,
+    '/images/some-image-2x.jpg' 2x,
+    '/images/some-image-3x.jpg' 3x
+  );
+}
+```
+
+```css
+a {
+  background-image: my-image-set(
+    '/images/some-image-1x.jpg' 1x,
+    '/images/some-image-2x.jpg' 2x,
+    '/images/some-image-3x.jpg' 3x
+  );
+}
+```
+
+```css
+a {
+  background-image: YoUr-image-set(
+    '/images/some-image-1x.jpg' 1x,
+    '/images/some-image-2x.jpg' 2x,
+    '/images/some-image-3x.jpg' 3x
+  );
+}
+```
diff --git a/lib/rules/unit-no-unknown/__tests__/index.js b/lib/rules/unit-no-unknown/__tests__/index.js
index e984faa7b4..8e5b1ac055 100644
--- a/lib/rules/unit-no-unknown/__tests__/index.js
+++ b/lib/rules/unit-no-unknown/__tests__/index.js
@@ -472,3 +472,30 @@ testRule(rule, {
     }
   ]
 });
+
+testRule(rule, {
+  ruleName,
+  config: [true, { ignoreFunctions: ["image-set", "/^my-/", "/^YOUR-/i"] }],
+
+  accept: [
+    {
+      code:
+        "a { background-image: image-set('/images/some-image-1x.jpg' 1x,'/images/some-image-2x.jpg' 2x,'/images/some-image-3x.jpg' 3x,); }"
+    },
+    {
+      code:
+        "a { background-image: my-image-set('/images/some-image-1x.jpg' 1x,'/images/some-image-2x.jpg' 2x,'/images/some-image-3x.jpg' 3x,); }"
+    },
+    {
+      code:
+        "a { background-image: YoUr-image-set('/images/some-image-1x.jpg' 1x,'/images/some-image-2x.jpg' 2x,'/images/some-image-3x.jpg' 3x,); }"
+    }
+  ],
+
+  reject: [
+    {
+      code: "a { margin: calc(10pixels + 1pixels); }",
+      message: messages.rejected("pixels")
+    }
+  ]
+});
diff --git a/lib/rules/unit-no-unknown/index.js b/lib/rules/unit-no-unknown/index.js
index a36ab16d9b..9674fc8a07 100644
--- a/lib/rules/unit-no-unknown/index.js
+++ b/lib/rules/unit-no-unknown/index.js
@@ -26,7 +26,8 @@ const rule = function(actual, options) {
       {
         actual: options,
         possible: {
-          ignoreUnits: [_.isString]
+          ignoreUnits: [_.isString],
+          ignoreFunctions: [_.isString]
         },
         optional: true
       }
@@ -42,9 +43,11 @@ const rule = function(actual, options) {
       value = value.replace(/\*/g, ",");
       valueParser(value).walk(function(valueNode) {
         // Ignore wrong units within `url` function
+        // and within functions listed in the `ignoreFunctions` option
         if (
           valueNode.type === "function" &&
-          valueNode.value.toLowerCase() === "url"
+          (valueNode.value.toLowerCase() === "url" ||
+            optionsMatches(options, "ignoreFunctions", valueNode.value))
         ) {
           return false;
         }