diff --git a/packages/postcss-merge-longhand/src/__tests__/boxBase.js b/packages/postcss-merge-longhand/src/__tests__/boxBase.js
index fa9363d06..2496f4aa5 100644
--- a/packages/postcss-merge-longhand/src/__tests__/boxBase.js
+++ b/packages/postcss-merge-longhand/src/__tests__/boxBase.js
@@ -117,6 +117,10 @@ addTests({
     message: 'should not explode box props with custom properties',
     fixture: 'h1{box-bottom:var(--variable)}',
     expected: 'h1{box-bottom:var(--variable)}',
+}, {
+    message: 'should preserve case of custom properties',
+    fixture: 'h1{box-top:10px;box-right:var(--fooBar);box-right:15px;box-bottom:var(--fooBar);box-bottom:20px;box-left:25px;box-top:var(--fooBar);box-left:var(--fooBar)}',
+    expected: 'h1{box:10px 15px 20px 25px;box-top:var(--fooBar);box-left:var(--fooBar)}',
 }, {
     message: 'should not merge incomplete box props where one has an unset property',
     fixture: 'h1{box-bottom:10px;box-top:unset;box-left:20px}',
diff --git a/packages/postcss-merge-longhand/src/__tests__/columns.js b/packages/postcss-merge-longhand/src/__tests__/columns.js
index 87e69fb7e..2a33f908f 100644
--- a/packages/postcss-merge-longhand/src/__tests__/columns.js
+++ b/packages/postcss-merge-longhand/src/__tests__/columns.js
@@ -82,3 +82,10 @@ test(
     passthroughCSS,
     'h1{columns:var(--variable)}',
 );
+
+test(
+    'should preserve case of custom properties',
+    passthroughCSS,
+    'h1{columns:var(--fooBar)}',
+);
+