diff --git a/al_function.hpp b/al_function.hpp
index b80f1c8..4d845cc 100644
--- a/al_function.hpp
+++ b/al_function.hpp
@@ -102,7 +102,7 @@ class Function {
                 case 4:
                     mask = mask_4;
                     remains = remains_4;
-                    shift = shift_3;
+                    shift = shift_4;
                     break;
                 default:
                     assert(false);
diff --git a/main.cpp b/main.cpp
index 450dc99..3570545 100644
--- a/main.cpp
+++ b/main.cpp
@@ -42,6 +42,8 @@ void test_function() {
     assert(("f(x_1 + 1 + 1, x_2, x_3) == f", negation == negation.var_negation(1).var_negation(1)));
     assert(("f(x_1, x_2 + 1 + 1, x_3) == f", negation == negation.var_negation(2).var_negation(2)));
     assert(("f(x_1, x_2, x_3 + 1 + 1) == f", negation == negation.var_negation(3).var_negation(3)));
+    assert((Function<uint16_t, 16>("0000000100010111").var_negation(1).string() == "0000001000101011"));
+    assert((Function<uint16_t, 16>("0000000100010111").var_negation(4).string() == "0001011100000001"));
     /*
     cout << "f(x_1, x_2, x_3)         = " << negation.string() << endl;
     cout << "f(x_1 + 1, x_2, x_3)     = " << negation.var_negation(1).string() << endl;