diff --git a/compiler/backend/src/org/jetbrains/jet/codegen/optimization/boxing/BoxingInterpreter.java b/compiler/backend/src/org/jetbrains/jet/codegen/optimization/boxing/BoxingInterpreter.java
index 8ede7fcda57..32b01ebc60c 100644
--- a/compiler/backend/src/org/jetbrains/jet/codegen/optimization/boxing/BoxingInterpreter.java
+++ b/compiler/backend/src/org/jetbrains/jet/codegen/optimization/boxing/BoxingInterpreter.java
@@ -211,12 +211,20 @@ public class BoxingInterpreter extends OptimizationBasicInterpreter {
             return v;
         }
 
-        if (v instanceof BoxedBasicValue && w != BasicValue.UNINITIALIZED_VALUE) {
+        if (v instanceof BoxedBasicValue && w == BasicValue.UNINITIALIZED_VALUE) {
+            return v;
+        }
+
+        if (w instanceof BoxedBasicValue && v == BasicValue.UNINITIALIZED_VALUE) {
+            return w;
+        }
+
+        if (v instanceof BoxedBasicValue) {
             onMergeFail((BoxedBasicValue) v);
             v = new BasicValue(v.getType());
         }
 
-        if (w instanceof BoxedBasicValue && v != BasicValue.UNINITIALIZED_VALUE) {
+        if (w instanceof BoxedBasicValue) {
             onMergeFail((BoxedBasicValue) w);
             w = new BasicValue(w.getType());
         }