diff --git a/integration-tests/public/complex-storage-structures/.gitignore b/integration-tests/public/complex-storage-structures/.gitignore
deleted file mode 100755
index 8de8f877e4..0000000000
--- a/integration-tests/public/complex-storage-structures/.gitignore
+++ /dev/null
@@ -1,9 +0,0 @@
-# Ignore build artifacts from the local tests sub-crate.
-/target/
-
-# Ignore backup files creates by cargo fmt.
-**/*.rs.bk
-
-# Remove Cargo.lock when creating an executable, leave it for libraries
-# More information here http://doc.crates.io/guide.html#cargotoml-vs-cargolock
-Cargo.lock
diff --git a/integration-tests/public/complex-storage-structures/Cargo.toml b/integration-tests/public/complex-storage-structures/Cargo.toml
index 8c637882cf..934a1ec064 100644
--- a/integration-tests/public/complex-storage-structures/Cargo.toml
+++ b/integration-tests/public/complex-storage-structures/Cargo.toml
@@ -6,10 +6,12 @@ edition = "2021"
 publish = false
 
 [dependencies]
-ink = { path = "../../crates/ink", default-features = false }
+ink = { path = "../../../crates/ink", default-features = false }
+scale = { package = "parity-scale-codec", version = "3.6.12", default-features = false, features = ["derive"] }
+scale-info = { version = "2.11", default-features = false }
 
 [dev-dependencies]
-ink_e2e = { path = "../../crates/e2e" }
+ink_e2e = { path = "../../../crates/e2e" }
 
 [lib]
 path = "lib.rs"
diff --git a/integration-tests/public/complex-storage-structures/lib.rs b/integration-tests/public/complex-storage-structures/lib.rs
index 37d832067d..6193ce0771 100644
--- a/integration-tests/public/complex-storage-structures/lib.rs
+++ b/integration-tests/public/complex-storage-structures/lib.rs
@@ -1,4 +1,4 @@
-#![cfg_attr(not(feature = "std"), no_std)]
+#![cfg_attr(not(feature = "std"), no_std, no_main)]
 
 #[ink::contract]
 pub mod complex_structures {
@@ -18,7 +18,7 @@ pub mod complex_structures {
     #[derive(Storable, StorableHint, StorageKey, Default, Debug)]
     #[cfg_attr(
         feature = "std",
-        derive(scale_info::TypeInfo, ink::storage::traits::StorageLayout)
+        derive(ink::scale_info::TypeInfo, ink::storage::traits::StorageLayout)
     )]
     pub struct TokenManagement {
         balances: Balances,
@@ -31,10 +31,10 @@ pub mod complex_structures {
         allowances: Mapping<(AccountId, AccountId), Balance, AutoKey>,
     }
 
-    #[derive(scale::Encode, scale::Decode, Default, Debug)]
+    #[derive(ink::scale::Encode, ink::scale::Decode, Default, Debug)]
     #[cfg_attr(
         feature = "std",
-        derive(scale_info::TypeInfo, ink::storage::traits::StorageLayout)
+        derive(ink::scale_info::TypeInfo, ink::storage::traits::StorageLayout)
     )]
     pub struct Balances {
         pub balance_state: u128,
@@ -42,7 +42,7 @@ pub mod complex_structures {
 
     impl<KEY: StorageKey> Allowances<KEY> {
         fn get_allowance(&self, owner: AccountId, spender: AccountId) -> Balance {
-            self.allowances.get(&(owner, spender)).unwrap_or(0)
+            self.allowances.get((owner, spender)).unwrap_or(0)
         }
 
         fn set_allowance(
@@ -51,7 +51,7 @@ pub mod complex_structures {
             spender: AccountId,
             value: Balance,
         ) {
-            self.allowances.insert(&(owner, spender), &value);
+            self.allowances.insert((owner, spender), &value);
         }
     }
 
@@ -69,12 +69,20 @@ pub mod complex_structures {
 
         #[ink(message)]
         pub fn increase_balances_state(&mut self, amount: u128) {
-            self.token_management.balances.balance_state += amount;
+            self.token_management
+                .balances
+                .balance_state
+                .checked_add(amount)
+                .expect("addition failed");
         }
 
         #[ink(message)]
         pub fn decrease_balances_state(&mut self, amount: u128) {
-            self.token_management.balances.balance_state -= amount;
+            self.token_management
+                .balances
+                .balance_state
+                .checked_sub(amount)
+                .expect("subtraction failed");
         }
 
         #[ink(message)]