diff --git a/src/lib/transform.js b/src/lib/transform.js
index 78bff2e..17fd276 100644
--- a/src/lib/transform.js
+++ b/src/lib/transform.js
@@ -7,7 +7,7 @@ const { parser } = require('../parser.js');
 const reducer = require('./reducer.js');
 const stringifier = require('./stringifier.js');
 
-const MATCH_CALC = /((?:-(moz|webkit)-)?calc)/i;
+const MATCH_CALC = /((?:-(moz|webkit)-)?calc(?!-))/i;
 
 /**
  * @param {string} value
diff --git a/test/index.js b/test/index.js
index a2f3d16..a1ebe82 100644
--- a/test/index.js
+++ b/test/index.js
@@ -30,6 +30,18 @@ function testCss(fixture, expected, opts = {}) {
   };
 }
 
+function testCssDoesNotThrow(fixture, expected, opts = {}) {
+  return async () => {
+    const result = await postcss(reduceCalc(opts)).process(
+      fixture,
+      postcssOpts
+    );
+    assert.strictEqual(result.css, expected);
+    const warnings = result.warnings();
+    assert.strictEqual(warnings.length, 0);
+  };
+}
+
 function testThrows(fixture, expected, warning, opts = {}) {
   fixture = `foo{bar:${fixture}}`;
   expected = `foo{bar:${expected}}`;
@@ -970,6 +982,11 @@ test(
   testValue('calc(1px + 2unknown)', 'calc(1px + 2unknown)')
 );
 
+test(
+  'calc-size should be ignored',
+  testCssDoesNotThrow('.foo{block-size: calc-size(auto, size)}', '.foo{block-size: calc-size(auto, size)}')
+);
+
 test(
   'error with parsing',
   testThrows(