diff --git a/yarn-project/foundation/src/abi/decoder.ts b/yarn-project/foundation/src/abi/decoder.ts
index 3cba542cb49d..35ac4e9c7ca9 100644
--- a/yarn-project/foundation/src/abi/decoder.ts
+++ b/yarn-project/foundation/src/abi/decoder.ts
@@ -24,11 +24,30 @@ class AbiDecoder {
     switch (abiType.kind) {
       case 'field':
         return this.getNextField().toBigInt();
-      case 'integer':
+      case 'integer': {
+        const nextField = this.getNextField();
+
         if (abiType.sign === 'signed') {
-          throw new Error('Unsupported type: signed integer');
+          // We get the last (width / 8) bytes where width = bits of type (i64, i32 etc)
+          const buf = nextField.toBuffer().subarray(-(abiType.width / 8));
+
+          // We then parse the buffer using 2's complement
+
+          // If our most significant bit is high
+          if (0x80 & buf.subarray(0, 1).readUInt8()) {
+            // We flip the bits
+            for (let i = 0; i < buf.length; i++) {
+              buf[i] = ~buf[i];
+            }
+
+            // Add one, then negate it
+            return -(BigInt(buf.toString('hex')) + 1n);
+          }
+
+          return BigInt(buf.toString('hex'));
         }
-        return this.getNextField().toBigInt();
+        return nextField.toBigInt();
+      }
       case 'boolean':
         return !this.getNextField().isZero();
       case 'array': {