diff --git a/src/__tests__/index.js b/src/__tests__/index.js
index 2293653..a585478 100644
--- a/src/__tests__/index.js
+++ b/src/__tests__/index.js
@@ -695,6 +695,13 @@ test(
   'calc(var(--xxx, var(--yyy))/2)',
 );
 
+test(
+  'nested var level (3rd-level) (#77, cssnano#880)',
+  testValue,
+  'calc(var(--xxx, var(--yyy, var(---zzz))) / 2)',
+  'calc(var(--xxx, var(--yyy, var(---zzz)))/2)',
+);
+
 test(
   'should not throw an exception when unknow function exist in calc',
   testValue,
diff --git a/src/parser.jison b/src/parser.jison
index eb402b8..00946e1 100644
--- a/src/parser.jison
+++ b/src/parser.jison
@@ -10,7 +10,7 @@
 
 (\-(webkit|moz)\-)?calc\b                       return 'CALC';
 
-[a-z][a-z0-9-]*\s*\((?:(?:\"(?:\\.|[^\"\\])*\"|\'(?:\\.|[^\'\\])*\')|\([^)]*\)|[^\(\)]*)*\)     return 'FUNCTION';
+[a-z][a-z0-9-]*\s*\((?:(?:\"(?:\\.|[^\"\\])*\"|\'(?:\\.|[^\'\\])*\')|\((?:[^)(]|\((?:[^)(]|\([^)(]*\))*\))*\)|[^\(\)]*)*\)     return 'FUNCTION';
 
 "*"                                             return 'MUL';
 "/"                                             return 'DIV';