diff --git a/teavm-core/src/main/java/org/teavm/javascript/Renderer.java b/teavm-core/src/main/java/org/teavm/javascript/Renderer.java
index a74505f75..e1e24e13f 100644
--- a/teavm-core/src/main/java/org/teavm/javascript/Renderer.java
+++ b/teavm-core/src/main/java/org/teavm/javascript/Renderer.java
@@ -63,7 +63,7 @@ public class Renderer implements ExprVisitor, StatementVisitor, RenderingContext
                         Object.class, "monitorEnter", Object.class, void.class);
                 
                 writer.appendMethodBody(monitorEnterRef).append("(");
-                statement.acceptVisitor(this);
+                statement.getObjectRef().acceptVisitor(this);
                 writer.append(");").softNewLine();
                 
             } catch (IOException ex){
@@ -80,7 +80,7 @@ public class Renderer implements ExprVisitor, StatementVisitor, RenderingContext
                         Object.class, "monitorExit", Object.class, void.class);
 
                 writer.appendMethodBody(monitorExitRef).append("(");
-                statement.acceptVisitor(this);
+                statement.getObjectRef().acceptVisitor(this);
                 writer.append(");").softNewLine();
             } catch (IOException ex){
                 throw new RenderingException("IO error occured", ex);
diff --git a/teavm-core/src/main/java/org/teavm/model/InstructionReadVisitor.java b/teavm-core/src/main/java/org/teavm/model/InstructionReadVisitor.java
index 446953241..5d7627469 100644
--- a/teavm-core/src/main/java/org/teavm/model/InstructionReadVisitor.java
+++ b/teavm-core/src/main/java/org/teavm/model/InstructionReadVisitor.java
@@ -204,11 +204,11 @@ class InstructionReadVisitor implements InstructionVisitor {
 
     @Override
     public void visit(MonitorEnterInstruction insn) {
-        
+        reader.monitorEnter(insn.getObjectRef());
     }
 
     @Override
     public void visit(MonitorExitInstruction insn) {
-        
+        reader.monitorExit(insn.getObjectRef());
     }
 }