diff --git a/lib/Less/Parser.php b/lib/Less/Parser.php
index ef8a8164..c788e153 100644
--- a/lib/Less/Parser.php
+++ b/lib/Less/Parser.php
@@ -2134,7 +2134,7 @@ private function parseAlpha() {
 		}
 
 		$value = $this->matchReg( '/\\G[0-9]+/' );
-		if ( !$value ) {
+		if ( $value === null ) {
 			$value = $this->expect( 'parseEntitiesVariable', 'Could not parse alpha' );
 		}
 
diff --git a/test/Fixtures/less.php/css/T371606-alpha-zero-error.css b/test/Fixtures/less.php/css/T371606-alpha-zero-error.css
new file mode 100644
index 00000000..5656bcf7
--- /dev/null
+++ b/test/Fixtures/less.php/css/T371606-alpha-zero-error.css
@@ -0,0 +1,3 @@
+.alpha {
+  filter: alpha(opacity=0);
+}
diff --git a/test/Fixtures/less.php/less/T371606-alpha-zero-error.less b/test/Fixtures/less.php/less/T371606-alpha-zero-error.less
new file mode 100644
index 00000000..0c7fd30d
--- /dev/null
+++ b/test/Fixtures/less.php/less/T371606-alpha-zero-error.less
@@ -0,0 +1,3 @@
+.alpha {
+	filter: alpha(opacity=0);
+  }