diff --git a/core/src/main/java/org/teavm/backend/wasm/WasmRuntime.java b/core/src/main/java/org/teavm/backend/wasm/WasmRuntime.java
index 2e38dfb56..93bfe1ba1 100644
--- a/core/src/main/java/org/teavm/backend/wasm/WasmRuntime.java
+++ b/core/src/main/java/org/teavm/backend/wasm/WasmRuntime.java
@@ -244,9 +244,10 @@ public final class WasmRuntime {
     }
 
     public static Address allocStack(int size) {
-        Address result = stack;
-        stack = stack.add((size + 1) << 2);
-        stack.add(-4).putInt(size);
+        Address result = stack.add(4);
+        stack = result.add(size << 2);
+        fillZero(result, size << 2);
+        stack.putInt(size);
         return result;
     }
 
@@ -256,7 +257,11 @@ public final class WasmRuntime {
 
     public static Address getNextStackRoots(Address address) {
         int size = address.getInt() + 1;
-        return address.add(-size * 4);
+        Address result = address.add(-size * 4);
+        if (result == initStack()) {
+            result = null;
+        }
+        return result;
     }
 
     public static int getStackRootCount(Address address) {
diff --git a/core/src/main/java/org/teavm/backend/wasm/generate/WasmGenerationVisitor.java b/core/src/main/java/org/teavm/backend/wasm/generate/WasmGenerationVisitor.java
index a4894073b..4de48bf91 100644
--- a/core/src/main/java/org/teavm/backend/wasm/generate/WasmGenerationVisitor.java
+++ b/core/src/main/java/org/teavm/backend/wasm/generate/WasmGenerationVisitor.java
@@ -906,8 +906,10 @@ class WasmGenerationVisitor implements StatementVisitor, ExprVisitor {
         }
 
         int offset = classGenerator.getFieldOffset(new FieldReference(WasmRuntime.class.getName(), "stack"));
-        result = new WasmStoreInt32(4, new WasmInt32Constant(offset), new WasmGetLocal(stackVariable),
-                WasmInt32Subtype.INT32);
+        WasmExpression oldValue = new WasmGetLocal(stackVariable);
+        oldValue = new WasmIntBinary(WasmIntType.INT32, WasmIntBinaryOperation.SUB, oldValue,
+                new WasmInt32Constant(4));
+        result = new WasmStoreInt32(4, new WasmInt32Constant(offset), oldValue, WasmInt32Subtype.INT32);
     }
 
     private void generateRegisterGcRoot(Expr slotExpr, Expr gcRootExpr) {
diff --git a/core/src/main/java/org/teavm/model/lowlevel/ClassInitializerTransformer.java b/core/src/main/java/org/teavm/model/lowlevel/ClassInitializerTransformer.java
index 18199001d..61264c00c 100644
--- a/core/src/main/java/org/teavm/model/lowlevel/ClassInitializerTransformer.java
+++ b/core/src/main/java/org/teavm/model/lowlevel/ClassInitializerTransformer.java
@@ -98,8 +98,7 @@ public class ClassInitializerTransformer {
 
         InvokeInstruction checkInitialized = new InvokeInstruction();
         checkInitialized.setType(InvocationType.SPECIAL);
-        checkInitialized.setMethod(new MethodReference(Allocator.class, "isInitialized",
-                Class.class, boolean.class));
+        checkInitialized.setMethod(new MethodReference(Allocator.class, "isInitialized", Class.class, boolean.class));
         checkInitialized.getArguments().add(clsVariable);
         checkInitialized.setReceiver(initializedVariable);
         block.getInstructions().add(checkInitialized);
diff --git a/core/src/main/java/org/teavm/runtime/Allocator.java b/core/src/main/java/org/teavm/runtime/Allocator.java
index f528be033..b1ad8862c 100644
--- a/core/src/main/java/org/teavm/runtime/Allocator.java
+++ b/core/src/main/java/org/teavm/runtime/Allocator.java
@@ -33,7 +33,9 @@ public final class Allocator {
     }
 
     public static Address allocateArray(RuntimeClass tag, int size) {
-        int sizeInBytes = tag.itemType.size * size + Structure.sizeOf(RuntimeArray.class);
+        int itemSize = (tag.itemType.flags & RuntimeClass.PRIMITIVE) != 0 ? tag.itemType.size : 4;
+        int sizeInBytes = Address.align(Address.fromInt(Structure.sizeOf(RuntimeArray.class)), itemSize).toInt();
+        sizeInBytes += itemSize * size;
         sizeInBytes = Address.align(Address.fromInt(sizeInBytes), 4).toInt();
         Address result = GC.alloc(sizeInBytes).toAddress();
         fillZero(result, sizeInBytes);