diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index b6996ca..9ebc682 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -8,7 +8,8 @@
 
 Run this command to locally compile an XAHL Hook source file (inside ./contracts) from .c to .wasm code:
 
-`$ hooks-cli compile-c contracts-c build`
+`$ hooks-cli compile-c contracts-c/toolbox build`
+`$ hooks-cli compile-c contracts-c/txns build`
 
 You can also build a single hook with;
 
@@ -46,4 +47,4 @@ Run JS Hooks Integration tests
 
 Run single JS Hooks Integration test
 
-`$ yarn run test:integration-js test/integration-js/toolbox/base.test.ts`
\ No newline at end of file
+`$ yarn run test:integration-js test/integration-js/toolbox/base.test.ts`
diff --git a/src/Xrpld.ts b/src/Xrpld.ts
index 75b18a8..2c81a1c 100644
--- a/src/Xrpld.ts
+++ b/src/Xrpld.ts
@@ -53,8 +53,13 @@ export class Xrpld {
         txResponse?.result?.meta as TransactionMetadata
       )
       if (hookExecutions.executions.length === 1) {
+        let returnCode = BigInt(
+          `0x${hookExecutions.executions[0].HookReturnCode}`
+        )
+        if (returnCode & 0x8000000000000000n)
+          returnCode = -(returnCode & ~0x8000000000000000n)
         throw Error(
-          `${hookExecutions.executions[0].HookReturnCode}: ${hookExecutions.executions[0].HookReturnString}`
+          `${returnCode}: ${hookExecutions.executions[0].HookReturnString}`
         )
       }
       throw Error(JSON.stringify(hookExecutions.executions))
diff --git a/src/models/iHookExecutions.ts b/src/models/iHookExecutions.ts
index 3b5abbb..06f76f4 100644
--- a/src/models/iHookExecutions.ts
+++ b/src/models/iHookExecutions.ts
@@ -8,7 +8,7 @@ export interface iHookExecution {
   HookHash: string
   HookInstructionCount: string
   HookResult: number
-  HookReturnCode: number
+  HookReturnCode: string
   HookReturnString: string
   HookStateChangeCount: number
 }
diff --git a/test/integration-c/hooks/toolbox/filterOnXrp.test.ts b/test/integration-c/hooks/toolbox/filterOnXrp.test.ts
index 8652070..3d21b94 100644
--- a/test/integration-c/hooks/toolbox/filterOnXrp.test.ts
+++ b/test/integration-c/hooks/toolbox/filterOnXrp.test.ts
@@ -93,7 +93,7 @@ describe('filterOnXrp', () => {
     } catch (error: unknown) {
       if (error instanceof Error) {
         expect(error.message).toEqual(
-          'e: filter_on_xrp: Ignoring non XAH Transaction'
+          '14: filter_on_xrp: Ignoring non XAH Transaction'
         )
       }
     }
diff --git a/test/integration-c/hooks/toolbox/hookOnTT.test.ts b/test/integration-c/hooks/toolbox/hookOnTT.test.ts
index 89ff677..149d818 100644
--- a/test/integration-c/hooks/toolbox/hookOnTT.test.ts
+++ b/test/integration-c/hooks/toolbox/hookOnTT.test.ts
@@ -91,7 +91,7 @@ describe('hookOnTT', () => {
     } catch (error: unknown) {
       if (error instanceof Error) {
         expect(error.message).toEqual(
-          'f: hook_on_tt: HookOn field is incorrectly set.'
+          '15: hook_on_tt: HookOn field is incorrectly set.'
         )
       }
     }
diff --git a/test/integration-c/hooks/toolbox/stateForeignBasic.test.ts b/test/integration-c/hooks/toolbox/stateForeignBasic.test.ts
index 80a3d88..08fc2a4 100644
--- a/test/integration-c/hooks/toolbox/stateForeignBasic.test.ts
+++ b/test/integration-c/hooks/toolbox/stateForeignBasic.test.ts
@@ -131,7 +131,7 @@ describe('stateForeignBasic', () => {
       })
     } catch (error: any) {
       expect(error.message).toEqual(
-        '22: state_foreign_basic: Could not get foreign state'
+        '34: state_foreign_basic: Could not get foreign state'
       )
     }
   })
@@ -208,7 +208,7 @@ describe('stateForeignBasic', () => {
       })
     } catch (error: any) {
       expect(error.message).toEqual(
-        '22: state_foreign_basic: Could not get foreign state'
+        '34: state_foreign_basic: Could not get foreign state'
       )
     }
   })
@@ -302,7 +302,7 @@ describe('stateForeignBasic', () => {
       })
     } catch (error: any) {
       expect(error.message).toEqual(
-        '27: state_foreign_basic: Could not set foreign state'
+        '39: state_foreign_basic: Could not set foreign state'
       )
     }
   })
diff --git a/test/integration-c/hooks/toolbox/utilSha512.test.ts b/test/integration-c/hooks/toolbox/utilSha512.test.ts
index 6b7dd44..46010cc 100644
--- a/test/integration-c/hooks/toolbox/utilSha512.test.ts
+++ b/test/integration-c/hooks/toolbox/utilSha512.test.ts
@@ -94,7 +94,7 @@ describe('utilSha512', () => {
         tx: builtTx,
       })
     } catch (error: any) {
-      expect(error.message).toEqual('35: util_sha512: Hashes do not match')
+      expect(error.message).toEqual('53: util_sha512: Hashes do not match')
     }
   })
 
@@ -170,7 +170,7 @@ describe('utilSha512', () => {
         tx: builtTx,
       })
     } catch (error: any) {
-      expect(error.message).toEqual('35: util_sha512: Hashes do not match')
+      expect(error.message).toEqual('53: util_sha512: Hashes do not match')
     }
   })
 
diff --git a/test/integration-js/hooks/toolbox/hookOnTT.js.test.ts b/test/integration-js/hooks/toolbox/hookOnTT.js.test.ts
index 03cb9b9..fe19a84 100644
--- a/test/integration-js/hooks/toolbox/hookOnTT.js.test.ts
+++ b/test/integration-js/hooks/toolbox/hookOnTT.js.test.ts
@@ -94,7 +94,7 @@ describe('hookOnTT', () => {
     } catch (error: unknown) {
       if (error instanceof Error) {
         expect(error.message).toEqual(
-          '8000000000000025: hookOnTT.ts: HookOn field is incorrectly set.'
+          '-37: hookOnTT.ts: HookOn field is incorrectly set.'
         )
       }
     }