diff --git a/src/printer-postcss.js b/src/printer-postcss.js
index ffb712db9..a83474c08 100644
--- a/src/printer-postcss.js
+++ b/src/printer-postcss.js
@@ -81,7 +81,7 @@ function genericPrint(path, options, print) {
 
       return concat([
         n.raws.before.replace(/[\s;]/g, ""),
-        n.prop.startsWith("--") ? n.prop : maybeToLowerCase(n.prop),
+        maybeToLowerCase(n.prop),
         ":",
         isValueExtend ? "" : " ",
         isComposed
@@ -482,7 +482,10 @@ function printNumber(rawNumber) {
 }
 
 function maybeToLowerCase(value) {
-  return value.includes("$") || value.includes("@") || value.includes("#")
+  return value.includes("$") ||
+  value.includes("@") ||
+  value.includes("#") ||
+  value.startsWith("--")
     ? value
     : value.toLowerCase();
 }
diff --git a/tests/css_case/__snapshots__/jsfmt.spec.js.snap b/tests/css_case/__snapshots__/jsfmt.spec.js.snap
index 5c8f6267a..92673f290 100644
--- a/tests/css_case/__snapshots__/jsfmt.spec.js.snap
+++ b/tests/css_case/__snapshots__/jsfmt.spec.js.snap
@@ -35,6 +35,9 @@ a[HREF=KeepAttrValue]:HOVER::FIRST-letter,
   }
 }
 
+@custom-media --KeepCustomMedia screen and (width >= 768px);
+@media (--KeepCustomMedia) {}
+
 @KeepDetachedRuleset: /*:*/ {
   BACKGROUND: RED;
 }
@@ -104,6 +107,10 @@ a[href="KeepAttrValue"]:hover::first-letter,
   }
 }
 
+@custom-media --KeepCustomMedia screen and (width >= 768px);
+@media (--KeepCustomMedia) {
+}
+
 @KeepDetachedRuleset: {
   background: RED;
 }
@@ -184,6 +191,9 @@ a[HREF=KeepAttrValue]:HOVER::FIRST-letter,
   }
 }
 
+@custom-media --KeepCustomMedia screen and (width >= 768px);
+@media (--KeepCustomMedia) {}
+
 @FUNCTION KeepFuncName() {
     @RETURN 12;
 }
@@ -256,6 +266,10 @@ a[href="KeepAttrValue"]:hover::first-letter,
   }
 }
 
+@custom-media --KeepCustomMedia screen and (width >= 768px);
+@media (--KeepCustomMedia) {
+}
+
 @function KeepFuncName() {
   @return 12;
 }
diff --git a/tests/css_case/case.less b/tests/css_case/case.less
index 41ab76ff0..9d8fe85a7 100644
--- a/tests/css_case/case.less
+++ b/tests/css_case/case.less
@@ -32,6 +32,9 @@ a[HREF=KeepAttrValue]:HOVER::FIRST-letter,
   }
 }
 
+@custom-media --KeepCustomMedia screen and (width >= 768px);
+@media (--KeepCustomMedia) {}
+
 @KeepDetachedRuleset: /*:*/ {
   BACKGROUND: RED;
 }
diff --git a/tests/css_case/case.scss b/tests/css_case/case.scss
index 8e7c4651d..f57543824 100644
--- a/tests/css_case/case.scss
+++ b/tests/css_case/case.scss
@@ -33,6 +33,9 @@ a[HREF=KeepAttrValue]:HOVER::FIRST-letter,
   }
 }
 
+@custom-media --KeepCustomMedia screen and (width >= 768px);
+@media (--KeepCustomMedia) {}
+
 @FUNCTION KeepFuncName() {
     @RETURN 12;
 }