diff -ur libsmi-0.5.0/lib/scanner-smi.h libsmi-0.5.0.new/lib/scanner-smi.h
--- libsmi-0.5.0/lib/scanner-smi.h	2019-01-07 11:17:38.000000000 +0300
+++ libsmi-0.5.0.new/lib/scanner-smi.h	2019-08-28 23:43:43.536880810 +0300
@@ -21,7 +21,7 @@
 #define YY_NO_UNPUT
 
 extern char *yytext;
-#if 0
+#ifndef yyleng
 extern int yyleng;
 #endif
 
diff -ur libsmi-0.5.0/lib/scanner-sming.h libsmi-0.5.0.new/lib/scanner-sming.h
--- libsmi-0.5.0/lib/scanner-sming.h	2019-01-07 11:17:38.000000000 +0300
+++ libsmi-0.5.0.new/lib/scanner-sming.h	2019-08-28 23:44:09.944050865 +0300
@@ -21,7 +21,9 @@
 #define YY_NO_UNPUT
 
 extern char *yytext;
+#ifndef yyleng
 extern int yyleng;
+#endif
 
 extern int smingEnterLexRecursion(FILE *file);
 extern void smingLeaveLexRecursion();
diff -ur libsmi-0.5.0/lib/scanner-yang.h libsmi-0.5.0.new/lib/scanner-yang.h
--- libsmi-0.5.0/lib/scanner-yang.h	2019-01-07 11:17:38.000000000 +0300
+++ libsmi-0.5.0.new/lib/scanner-yang.h	2019-08-28 23:44:33.840204000 +0300
@@ -21,8 +21,7 @@
 #define YY_NO_UNPUT
 
 extern char *yytext;
-#if 0
-/* this does not seem to be needed with flex 2.5.35 and in fact conflicts */
+#ifndef yyleng
 extern int yyleng;
 #endif