diff --git a/compiler/backend/src/org/jetbrains/jet/codegen/ExpressionCodegen.java b/compiler/backend/src/org/jetbrains/jet/codegen/ExpressionCodegen.java
index 0e0381ba4a8..e84cac2d840 100644
--- a/compiler/backend/src/org/jetbrains/jet/codegen/ExpressionCodegen.java
+++ b/compiler/backend/src/org/jetbrains/jet/codegen/ExpressionCodegen.java
@@ -3094,7 +3094,7 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> implem
 
         Type type = expressionType(expression.getBaseExpression());
         value.put(type, v);
-        callableMethod.invokeWithNotNullAssertion(v, state, resolvedCall);
+        invokeFunction(resolvedCall, StackValue.onStack(type));
 
         value.store(callableMethod.getReturnType(), v);
         value.put(type, v);
@@ -3163,8 +3163,8 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> implem
         else {
             ResolvedCall<?> resolvedCall = getResolvedCallWithAssert(expression, bindingContext);
             Callable callable = resolveToCallable((FunctionDescriptor) op, false);
+            invokeFunction(resolvedCall, StackValue.onStack(type));
             CallableMethod callableMethod = (CallableMethod) callable;
-            callableMethod.invokeWithNotNullAssertion(v, state, resolvedCall);
             storeType = callableMethod.getReturnType();
         }
 
diff --git a/compiler/testData/codegen/box/extensionFunctions/kt3969.kt b/compiler/testData/codegen/box/extensionFunctions/kt3969.kt
new file mode 100644
index 00000000000..95930acb52a
--- /dev/null
+++ b/compiler/testData/codegen/box/extensionFunctions/kt3969.kt
@@ -0,0 +1,19 @@
+var result = "Fail"
+
+class A
+
+fun A.inc(s: String = "OK"): A {
+    result = s
+    return this
+}
+
+fun box(): String {
+    var a = A()
+    a++
+    if (result != "OK") return "Fail 1"
+
+    result = "Fail"
+    ++a
+
+    return result
+}
\ No newline at end of file
diff --git a/compiler/tests/org/jetbrains/jet/codegen/generated/BlackBoxCodegenTestGenerated.java b/compiler/tests/org/jetbrains/jet/codegen/generated/BlackBoxCodegenTestGenerated.java
index 46538827d7e..201f48c9a39 100644
--- a/compiler/tests/org/jetbrains/jet/codegen/generated/BlackBoxCodegenTestGenerated.java
+++ b/compiler/tests/org/jetbrains/jet/codegen/generated/BlackBoxCodegenTestGenerated.java
@@ -2777,6 +2777,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             doTest(fileName);
         }
         
+        @TestMetadata("kt3969.kt")
+        public void testKt3969() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/extensionFunctions/kt3969.kt");
+            doTest(fileName);
+        }
+        
         @TestMetadata("kt4118.kt")
         public void testKt4118() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/extensionFunctions/kt4118.kt");