diff --git a/integration_tests/test_membership_01.py b/integration_tests/test_membership_01.py
index 0f3b2b0d94..10cb4f682e 100644
--- a/integration_tests/test_membership_01.py
+++ b/integration_tests/test_membership_01.py
@@ -35,7 +35,7 @@ def test_str_set():
     a: set[str] = {'a', 'b', 'c', 'e', 'f'}
     i: str
     assert ('a' in a)
-    # assert ('d' not in a)
+    assert ('d' not in a)
     i = 'c'
     assert (i in a)
 
diff --git a/src/libasr/codegen/llvm_utils.cpp b/src/libasr/codegen/llvm_utils.cpp
index c49640329f..dde91aa6d9 100644
--- a/src/libasr/codegen/llvm_utils.cpp
+++ b/src/libasr/codegen/llvm_utils.cpp
@@ -3393,8 +3393,13 @@ namespace LCompilers {
                            module, key_asr_type, true);
         }
         llvm_utils->start_new_block(mergeBB);
-        llvm::Value *flag = LLVM::CreateLoad(*builder, flag_ptr);
         llvm::Value *pos = LLVM::CreateLoad(*builder, pos_ptr);
+        llvm::Value* pos_mask_value = LLVM::CreateLoad(*builder,
+                                        llvm_utils->create_ptr_gep(key_mask, pos));
+        llvm::Value *flag = builder->CreateOr(
+            builder->CreateICmpEQ(pos_mask_value,
+            llvm::ConstantInt::get(llvm::Type::getInt8Ty(context), llvm::APInt(8, 0))),
+            LLVM::CreateLoad(*builder, flag_ptr));
         llvm::AllocaInst *is_key_matching_ptr = builder0.CreateAlloca(llvm::Type::getInt1Ty(context), nullptr);
 
         llvm_utils->create_if_else(flag, [&](){
@@ -6783,14 +6788,20 @@ namespace LCompilers {
                                     module, el_asr_type, true);
         }
         llvm_utils->start_new_block(mergeBB);
-        llvm::Value *flag = LLVM::CreateLoad(*builder, flag_ptr);
+
+        llvm::Value* pos = LLVM::CreateLoad(*builder, pos_ptr);
+        llvm::Value* pos_mask_value = LLVM::CreateLoad(*builder,
+                                        llvm_utils->create_ptr_gep(el_mask, pos));
+        llvm::Value *flag = builder->CreateOr(
+            builder->CreateICmpEQ(pos_mask_value,
+            llvm::ConstantInt::get(llvm::Type::getInt8Ty(context), llvm::APInt(8, 0))),
+            LLVM::CreateLoad(*builder, flag_ptr));
         llvm::AllocaInst *is_el_matching_ptr = builder0.CreateAlloca(llvm::Type::getInt1Ty(context), nullptr);
 
         llvm_utils->create_if_else(flag, [&](){
         LLVM::CreateStore(*builder, llvm::ConstantInt::get(llvm::Type::getInt1Ty(context), 0), is_el_matching_ptr);
             }, [&](){
         // Check if the actual element is present or not
-        llvm::Value* pos = LLVM::CreateLoad(*builder, pos_ptr);
         llvm::Value* item = llvm_utils->list_api->read_item(el_list, pos, false, module,
                     LLVM::is_llvm_struct(el_asr_type)) ;
         llvm::Value *iseq =llvm_utils->is_equal_by_value(el,