diff --git a/lib/compressor/compress/Dimension.js b/lib/compressor/compress/Dimension.js
index 6cfa693a..b69030fa 100644
--- a/lib/compressor/compress/Dimension.js
+++ b/lib/compressor/compress/Dimension.js
@@ -19,9 +19,9 @@ module.exports = function compressDimension(node, item) {
 
     node.value = value;
 
-    if (value === '0' && !NON_LENGTH_UNIT.hasOwnProperty(unit)) {
+    if (value === '0' && this.declaration && !NON_LENGTH_UNIT.hasOwnProperty(unit)) {
         // issue #200: don't remove units in flex property as it could change value meaning
-        if (this.declaration && this.declaration.property.name === 'flex') {
+        if (this.declaration.property.name === 'flex') {
             return;
         }
 
diff --git a/lib/compressor/compress/Value.js b/lib/compressor/compress/Value.js
index ed42670f..afcc02c9 100644
--- a/lib/compressor/compress/Value.js
+++ b/lib/compressor/compress/Value.js
@@ -3,6 +3,10 @@ var compressFontWeight = require('./property/font-weight.js');
 var compressBackground = require('./property/background.js');
 
 module.exports = function compressValue(node) {
+    if (!this.declaration) {
+        return;
+    }
+
     var property = this.declaration.property.name;
 
     if (/background$/.test(property)) {
diff --git a/test/fixture/compress/atrules/supports-2.css b/test/fixture/compress/atrules/supports-2.css
index f8f1deb6..75a84902 100644
--- a/test/fixture/compress/atrules/supports-2.css
+++ b/test/fixture/compress/atrules/supports-2.css
@@ -1,5 +1,5 @@
 /*
-    issue #273 should compress length dimension outside block
+    issue #273 shouldn't compress length dimension outside declaration
 */
 @supports (width: 0px) and (test: 0deg) {
     .test {
diff --git a/test/fixture/compress/atrules/supports-2.min.css b/test/fixture/compress/atrules/supports-2.min.css
index 97137201..c039ec82 100644
--- a/test/fixture/compress/atrules/supports-2.min.css
+++ b/test/fixture/compress/atrules/supports-2.min.css
@@ -1 +1 @@
-@supports (width:0) and (test:0deg){.test{foo:1}}
+@supports (width:0px) and (test:0deg){.test{foo:1}}