diff --git a/core/src/main/java/org/teavm/ast/optimization/OptimizingVisitor.java b/core/src/main/java/org/teavm/ast/optimization/OptimizingVisitor.java
index 5007ef45f..6171b349c 100644
--- a/core/src/main/java/org/teavm/ast/optimization/OptimizingVisitor.java
+++ b/core/src/main/java/org/teavm/ast/optimization/OptimizingVisitor.java
@@ -697,7 +697,9 @@ class OptimizingVisitor implements StatementVisitor, ExprVisitor {
             return false;
         }
         optimization.unwrappedArrayVariable = ((VariableExpr) assign.getLeftValue()).getIndex();
-        if (writeFrequencies[optimization.unwrappedArrayVariable] != 1) {
+        if (writeFrequencies[optimization.unwrappedArrayVariable] != 1
+                || preservedVars[optimization.unwrappedArrayVariable]
+                || readFrequencies[optimization.unwrappedArrayVariable] != optimization.arraySize) {
             return false;
         }
 
diff --git a/html4j/src/test/java/org/teavm/html4j/test/KnockoutTCKTest.java b/html4j/src/test/java/org/teavm/html4j/test/KnockoutTCKTest.java
index 9455677ae..cad0eeeec 100644
--- a/html4j/src/test/java/org/teavm/html4j/test/KnockoutTCKTest.java
+++ b/html4j/src/test/java/org/teavm/html4j/test/KnockoutTCKTest.java
@@ -21,7 +21,6 @@ import net.java.html.json.tests.KnockoutTest;
 import net.java.html.json.tests.MinesTest;
 import net.java.html.json.tests.OperationsTest;
 import net.java.html.json.tests.WebSocketTest;
-import org.junit.Ignore;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.teavm.junit.SkipJVM;
@@ -35,7 +34,6 @@ import org.teavm.junit.WholeClassCompilation;
 @RunWith(TeaVMTestRunner.class)
 @SkipJVM
 @WholeClassCompilation
-@Ignore
 public class KnockoutTCKTest {
     private final ConvertTypesTest convertTypesTest = new ConvertTypesTest();
     private final JSONTest jsonTest = new JSONTest();