diff --git a/Makefile b/Makefile
index fed1aeb629..bc9d171bd6 100644
--- a/Makefile
+++ b/Makefile
@@ -81,8 +81,8 @@ build-nym-cli:
 
 wasm:
 	RUSTFLAGS='-C link-arg=-s' cargo build --manifest-path contracts/Cargo.toml --release --target wasm32-unknown-unknown
-	wasm-opt -Os contracts/target/wasm32-unknown-unknown/release/vesting_contract.wasm -o contracts/target/wasm32-unknown-unknown/release/vesting_contract.wasm
-	wasm-opt -Os contracts/target/wasm32-unknown-unknown/release/mixnet_contract.wasm -o contracts/target/wasm32-unknown-unknown/release/mixnet_contract.wasm
+	wasm-opt --disable-sign-ext -Os contracts/target/wasm32-unknown-unknown/release/vesting_contract.wasm -o contracts/target/wasm32-unknown-unknown/release/vesting_contract.wasm
+	wasm-opt --disable-sign-ext -Os contracts/target/wasm32-unknown-unknown/release/mixnet_contract.wasm -o contracts/target/wasm32-unknown-unknown/release/mixnet_contract.wasm
 
 # NOTE: this seems deprecated an not needed anymore?
 mixnet-opt: wasm
diff --git a/contracts/mixnet/Makefile b/contracts/mixnet/Makefile
index 93032c5c3e..7741d05913 100644
--- a/contracts/mixnet/Makefile
+++ b/contracts/mixnet/Makefile
@@ -1,5 +1,5 @@
 opt: wasm
-	wasm-opt -Os ../target/wasm32-unknown-unknown/release/mixnet_contract.wasm -o ../target/wasm32-unknown-unknown/release/mixnet_contract.wasm
+	wasm-opt --disable-sign-ext -Os ../target/wasm32-unknown-unknown/release/mixnet_contract.wasm -o ../target/wasm32-unknown-unknown/release/mixnet_contract.wasm
 
 wasm:
 	RUSTFLAGS='-C link-arg=-s' cargo build --release --target wasm32-unknown-unknown