diff --git a/src/__tests__/index.js b/src/__tests__/index.js
index 75bc10f..1f32b83 100644
--- a/src/__tests__/index.js
+++ b/src/__tests__/index.js
@@ -47,6 +47,10 @@ it('allows undefined values', () => {
   })
 })
 
+it('allows CSS custom properties to pass through', () => {
+  expect(transformCss([['--my-prop', '0%']])).toEqual({ '--my-prop': '0%' })
+})
+
 it('allows percent in unspecialized transform', () => {
   expect(transformCss([['top', '0%']])).toEqual({ top: '0%' })
 })
diff --git a/src/index.js b/src/index.js
index 2b678f6..0f1ad9c 100644
--- a/src/index.js
+++ b/src/index.js
@@ -59,7 +59,13 @@ export const getStylesForProperty = (propName, inputValue, allowShorthand) => {
     : { [propName]: propValue }
 }
 
-export const getPropertyName = camelizeStyleName
+export const getPropertyName = propName => {
+  const isCustomProp = /^--\w+/.test(propName)
+  if (isCustomProp) {
+    return propName
+  }
+  return camelizeStyleName(propName)
+}
 
 export default (rules, shorthandBlacklist = []) =>
   rules.reduce((accum, rule) => {