diff --git a/lesscpy/lessc/lexer.py b/lesscpy/lessc/lexer.py
index 4b876e1..78d7ecd 100644
--- a/lesscpy/lessc/lexer.py
+++ b/lesscpy/lessc/lexer.py
@@ -35,6 +35,7 @@ class LessLexer:
         'css_important',
         'css_vendor_hack',
         'css_uri',
+        'css_ms_filter',
         
         'less_variable',
         'less_comment',
@@ -83,6 +84,10 @@ class LessLexer:
         '|(not|lang|nth-[a-z\-]+)\(.+\)'
         '|and[ \t]\(.+\)')
         return t
+    
+    def t_css_ms_filter(self, t):
+        r'progid:[^;]*'
+        return t
         
     def t_css_ident(self, t):
         (r'([\-\.\#]?'
diff --git a/lesscpy/lessc/parser.py b/lesscpy/lessc/parser.py
index 4846e10..a27b4fd 100644
--- a/lesscpy/lessc/parser.py
+++ b/lesscpy/lessc/parser.py
@@ -373,6 +373,7 @@ class LessParser(object):
                                     | vendor_property
                                     | istring
                                     | fcall
+                                    | css_ms_filter
         """
         p[0] = p[1]
         
diff --git a/lesscpy/scripts/compiler.py b/lesscpy/scripts/compiler.py
index 26152ed..f87ffd1 100644
--- a/lesscpy/scripts/compiler.py
+++ b/lesscpy/scripts/compiler.py
@@ -41,9 +41,9 @@ def ldirectory(inpath, outpath, args, scope):
             recompile = True
         if recompile:
             if args.verbose: print("%s -> %s" % (lf, outf))
-            p = parser.LessParser(yacc_debug=False,
+            p = parser.LessParser(yacc_debug=(args.debug),
                                   lex_optimize=True,
-                                  yacc_optimize=True,
+                                  yacc_optimize=(not args.debug),
                                   scope=scope,
                                   tabfile=yacctab,
                                   verbose=args.verbose)
@@ -112,10 +112,9 @@ def run():
     scope = None
     if args.include:
         for u in args.include.split(','):
-            p = parser.LessParser(
-                                  yacc_debug=False,
+            p = parser.LessParser(yacc_debug=(args.debug),
                                   lex_optimize=True,
-                                  yacc_optimize=True,
+                                  yacc_optimize=(not args.debug),
                                   tabfile=yacctab,
                                   verbose=args.verbose)
             p.parse(filename=u, debuglevel=0)
diff --git a/lesscpy/test/css/imports.css b/lesscpy/test/css/imports.css
index 278d53a..ea3323b 100644
--- a/lesscpy/test/css/imports.css
+++ b/lesscpy/test/css/imports.css
@@ -2,6 +2,12 @@
 @import 'some/other.css.file.CSS';
 @import 'some.css' all;
 @import "some.print.css" print;
+.mixin {
+	color: red;
+}
+.mixin {
+	color: red;
+}
 .import {
 	color: red;
 	width: 6px;
diff --git a/lesscpy/test/css/imports.min.css b/lesscpy/test/css/imports.min.css
index 76d6d53..b7a21dd 100644
--- a/lesscpy/test/css/imports.min.css
+++ b/lesscpy/test/css/imports.min.css
@@ -2,4 +2,6 @@
 @import 'some/other.css.file.CSS';
 @import 'some.css' all;
 @import "some.print.css" print;
+.mixin{color:red;}
+.mixin{color:red;}
 .import{color:red;width:6px;height:9px;}