diff --git a/packages/stylelint-config-wordpress/__tests__/functions-invalid.css b/packages/stylelint-config-wordpress/__tests__/functions-invalid.css
new file mode 100644
index 0000000000000..33a93985335cf
--- /dev/null
+++ b/packages/stylelint-config-wordpress/__tests__/functions-invalid.css
@@ -0,0 +1,5 @@
+/* function-name-case */
+
+a {
+	width: Calc(5% - 10em);
+}
diff --git a/packages/stylelint-config-wordpress/__tests__/functions-valid.css b/packages/stylelint-config-wordpress/__tests__/functions-valid.css
new file mode 100644
index 0000000000000..8219b38b2005c
--- /dev/null
+++ b/packages/stylelint-config-wordpress/__tests__/functions-valid.css
@@ -0,0 +1,7 @@
+/* function-name-case */
+
+a {
+	width: calc(5% - 10em);
+	filter: progid:DXImageTransform.Microsoft.gradient(startColorstr="#1e8cbe", endColorstr="#0074a2", GradientType=0);
+	filter: progid:DXImageTransform.Microsoft.Alpha(opacity=100);
+}
diff --git a/packages/stylelint-config-wordpress/__tests__/functions.js b/packages/stylelint-config-wordpress/__tests__/functions.js
new file mode 100644
index 0000000000000..b7cb3b65dbd12
--- /dev/null
+++ b/packages/stylelint-config-wordpress/__tests__/functions.js
@@ -0,0 +1,84 @@
+"use strict"
+
+const fs = require("fs")
+const config = require("../")
+const stylelint = require("stylelint")
+
+const validCss = fs.readFileSync("./__tests__/functions-valid.css", "utf-8")
+const invalidCss = fs.readFileSync("./__tests__/functions-invalid.css", "utf-8")
+
+describe("flags no warnings with valid functions css", () => {
+  let result
+
+  beforeEach(() => {
+    result = stylelint.lint({
+      code: validCss,
+      config,
+    })
+  })
+
+  it("did not error", () => {
+    return result.then(data => (
+      expect(data.errored).toBeFalsy()
+    ))
+  })
+
+  it("flags no warnings", () => {
+    return result.then(data => (
+      expect(data.results[0].warnings.length).toBe(0)
+    ))
+  })
+})
+
+describe("flags warnings with invalid functions css", () => {
+  let result
+
+  beforeEach(() => {
+    result = stylelint.lint({
+      code: invalidCss,
+      config,
+    })
+  })
+
+  it("did error", () => {
+    return result.then(data => (
+      expect(data.errored).toBeTruthy()
+    ))
+  })
+
+  it("flags three warnings", () => {
+    return result.then(data => (
+      expect(data.results[0].warnings.length).toBe(1)
+    ))
+  })
+
+  it("correct first warning text", () => {
+    return result.then(data => (
+      expect(data.results[0].warnings[0].text).toBe("Expected \"Calc\" to be \"calc\" (function-name-case)")
+    ))
+  })
+
+  it("correct first warning rule flagged", () => {
+    return result.then(data => (
+      expect(data.results[0].warnings[0].rule).toBe("function-name-case")
+    ))
+  })
+
+  it("correct first warning severity flagged", () => {
+    return result.then(data => (
+      expect(data.results[0].warnings[0].severity).toBe("error")
+    ))
+  })
+
+  it("correct first warning line number", () => {
+    return result.then(data => (
+      expect(data.results[0].warnings[0].line).toBe(4)
+    ))
+  })
+
+  it("correct first warning column number", () => {
+    return result.then(data => (
+      expect(data.results[0].warnings[0].column).toBe(9)
+    ))
+  })
+})
diff --git a/packages/stylelint-config-wordpress/index.js b/packages/stylelint-config-wordpress/index.js
index 13106e539770b..c71d12121649c 100644
--- a/packages/stylelint-config-wordpress/index.js
+++ b/packages/stylelint-config-wordpress/index.js
@@ -40,7 +40,9 @@ module.exports = {
     "function-comma-space-before": "never",
     "function-linear-gradient-no-nonstandard-direction": true,
     "function-max-empty-lines": 1,
-    "function-name-case": "lower",
+    "function-name-case": [ "lower", {
+      ignoreFunctions: ["/^DXImageTransform.Microsoft.*$/"],
+    } ],
     "function-parentheses-space-inside": "never",
     "function-url-quotes": "never",
     "function-whitespace-after": "always",