diff --git a/eval.c b/eval.c
index f58c4739..de858f87 100644
--- a/eval.c
+++ b/eval.c
@@ -837,6 +837,7 @@ static void generate_cnd (sexp ctx, sexp cnd) {
   sexp_context_depth(ctx)--;
   label1 = sexp_context_make_label(ctx);
   generate(ctx, sexp_cnd_pass(cnd));
+  sexp_context_tailp(ctx) = tailp;
   emit(ctx, SEXP_OP_JUMP);
   sexp_context_depth(ctx)--;
   label2 = sexp_context_make_label(ctx);
@@ -2354,6 +2355,18 @@ sexp sexp_define_foreign_aux (sexp ctx, sexp env, char *name, int num_args,
   return res;
 }
 
+sexp sexp_define_foreign_param (sexp ctx, sexp env, char *name, int num_args,
+                                sexp_proc1 f, char *param) {
+  sexp res;
+  sexp_gc_var1(tmp);
+  sexp_gc_preserve1(ctx, tmp);
+  tmp = sexp_intern(ctx, param);
+  tmp = sexp_env_cell(env, tmp);
+  res = sexp_define_foreign_aux(ctx, env, name, num_args, 3, f, tmp);
+  sexp_gc_release1(ctx);
+  return res;
+}
+
 #if SEXP_USE_TYPE_DEFS
 
 sexp sexp_make_type_predicate (sexp ctx, sexp name, sexp type) {
diff --git a/include/chibi/eval.h b/include/chibi/eval.h
index 60201c61..7ce70433 100644
--- a/include/chibi/eval.h
+++ b/include/chibi/eval.h
@@ -152,6 +152,8 @@ SEXP_API sexp sexp_define_foreign_aux (sexp ctx, sexp env, char *name, int num_a
 #define sexp_define_foreign(c,e,s,n,f) sexp_define_foreign_aux(c,e,s,n,0,(sexp_proc1)f,NULL)
 #define sexp_define_foreign_opt(c,e,s,n,f,d) sexp_define_foreign_aux(c,e,s,n,1,(sexp_proc1)f,d)
 
+SEXP_API sexp sexp_define_foreign_param (sexp ctx, sexp env, char *name, int num_args, sexp_proc1 f, char *param);
+
 #if SEXP_USE_TYPE_DEFS
 SEXP_API sexp sexp_make_type_predicate (sexp ctx, sexp name, sexp type);
 SEXP_API sexp sexp_make_constructor (sexp ctx, sexp name, sexp type);