diff --git a/assembler/src/gen4asm.h b/assembler/src/gen4asm.h
index 680a0a47..ea498bba 100644
--- a/assembler/src/gen4asm.h
+++ b/assembler/src/gen4asm.h
@@ -180,6 +180,7 @@ void insert_register(struct declared_register *reg);
 
 int yyparse(void);
 int yylex(void);
+int yylex_destroy(void);
 
 char *
 lex_text(void);
diff --git a/assembler/src/main.c b/assembler/src/main.c
index 28cca232..d2c57013 100644
--- a/assembler/src/main.c
+++ b/assembler/src/main.c
@@ -275,6 +275,8 @@ int main(int argc, char **argv)
 
 	err = yyparse();
 
+	yylex_destroy();
+
 	if (yyin)
 		fclose(yyin);