diff --git a/filter/config.Y b/filter/config.Y
index e01e02ef..cf499b66 100644
--- a/filter/config.Y
+++ b/filter/config.Y
@@ -304,12 +304,10 @@ f_generate_lc(struct f_inst *t1, struct f_inst *t2, struct f_inst *t3)
   }
   else
   {
-    rv = cfg_allocz(sizeof(struct f_inst3));
-    rv->lineno = ifs->lino;
-    rv->fi_code = FI_LC_CONSTRUCT;
+    rv = f_new_inst(FI_LC_CONSTRUCT);
     rv->a1.p = t1;
     rv->a2.p = t2;
-    INST3(rv).p = t3;
+    rv->a3.p = t3;
   }
 
   return rv;
diff --git a/filter/filter.c b/filter/filter.c
index 3d7b5c9f..7117da48 100644
--- a/filter/filter.c
+++ b/filter/filter.c
@@ -601,6 +601,8 @@ static struct tbf rl_runtime_err = TBF_DEFAULT_LOG_LIMITS;
 #define TWOARGS_C TWOARGS \
                   if (v1.type != v2.type) \
 		    runtime( "Can't operate with values of incompatible types" );
+#define THREEARGS TWOARGS \
+		  ARG(v3, a3.p)
 #define ACCESS_RTE \
   do { if (!f_rte) runtime("No route to access"); } while (0)
 
@@ -628,7 +630,7 @@ static struct f_val
 interpret(struct f_inst *what)
 {
   struct symbol *sym;
-  struct f_val v1, v2, res = { .type = T_VOID }, *vp;
+  struct f_val v1, v2, v3, res = { .type = T_VOID }, *vp;
   unsigned u1, u2;
   int i;
   u32 as;
@@ -749,12 +751,7 @@ interpret(struct f_inst *what)
 
   case FI_LC_CONSTRUCT:
     {
-      TWOARGS;
-
-      /* Third argument hack */
-      struct f_val v3 = interpret(INST3(what).p);
-      if (v3.type & T_RETURN)
-	return v3;
+      THREEARGS;
 
       if ((v1.type != T_INT) || (v2.type != T_INT) || (v3.type != T_INT))
 	runtime( "Can't operate with value of non-integer type in LC constructor" );
@@ -1664,9 +1661,7 @@ i_same(struct f_inst *f1, struct f_inst *f2)
   case FI_TYPE: ONEARG; break;
 
   case FI_LC_CONSTRUCT:
-    TWOARGS;
-    if (!i_same(INST3(f1).p, INST3(f2).p))
-      return 0;
+    THREEARGS;
     break;
 
   case FI_SET:
diff --git a/filter/filter.h b/filter/filter.h
index 694bdfd7..1e5fc8ff 100644
--- a/filter/filter.h
+++ b/filter/filter.h
@@ -93,6 +93,10 @@ struct f_inst {		/* Instruction */
     uint i;
     void *p;
   } a2;			/* The second argument */
+  union {
+    int i;
+    void *p;
+  } a3;			/* The third argument */
   int lineno;
 };
 
@@ -105,17 +109,6 @@ struct f_inst_roa_check {
   struct rtable_config *rtc;
 };
 
-struct f_inst3 {
-  struct f_inst i;
-  union {
-    int i;
-    void *p;
-  } a3;
-};
-
-#define INST3(x) (((struct f_inst3 *) x)->a3)
-
-
 struct f_prefix {
   net_addr net;
   u8 lo, hi;