diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7f27873..1cfeefc 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -36,6 +36,11 @@ add_custom_command(OUTPUT ${LEX_GENERATED_SOURCE_FILE}
         COMMENT "generate C source file for lexer"
         VERBATIM)
 
+# remove dependency when compiling with MSVC on windows
+if (MSVC)
+    add_compile_definitions(YY_NO_UNISTD_H)
+endif()
+
 # ------------------------------------------------ #
 #  Yacc                                            #
 # ------------------------------------------------ #
@@ -140,7 +145,7 @@ set_target_properties(check
 if (MSVC)
     set(CHECK_FLAGS /DEBUG /WX)
 else()
-    set(DEBUG_FLAGS -g /Werror)
+    set(DEBUG_FLAGS -g -Werror)
 endif()
 
 # compiler flags targeting a GCC debug environment
diff --git a/src/lex/lexer.l b/src/lex/lexer.l
index c1efd4f..8823195 100644
--- a/src/lex/lexer.l
+++ b/src/lex/lexer.l
@@ -12,9 +12,6 @@
 %option nounput
 %option noinput
 
-/* prevent depency of unistd.h */
-%option nounistd
-
 %%
 "\n"    yyLineNumber++;