diff --git a/src/neo/SmartContract/ApplicationEngine.cs b/src/neo/SmartContract/ApplicationEngine.cs
index 8b8daa6c62..6b00615624 100644
--- a/src/neo/SmartContract/ApplicationEngine.cs
+++ b/src/neo/SmartContract/ApplicationEngine.cs
@@ -58,7 +58,7 @@ protected ApplicationEngine(TriggerType trigger, IVerifiable container, StoreVie
             this.testMode = testMode;
         }
 
-        internal void AddGas(long gas)
+        protected internal void AddGas(long gas)
         {
             GasConsumed = checked(GasConsumed + gas);
             if (!testMode && GasConsumed > gas_amount)
@@ -217,12 +217,17 @@ public override void Dispose()
             base.Dispose();
         }
 
-        protected override void OnSysCall(uint method)
+        protected void ValidateCallFlags(InteropDescriptor descriptor)
         {
-            InteropDescriptor descriptor = services[method];
             ExecutionContextState state = CurrentContext.GetState<ExecutionContextState>();
             if (!state.CallFlags.HasFlag(descriptor.RequiredCallFlags))
                 throw new InvalidOperationException($"Cannot call this SYSCALL with the flag {state.CallFlags}.");
+        }
+
+        protected override void OnSysCall(uint method)
+        {
+            InteropDescriptor descriptor = services[method];
+            ValidateCallFlags(descriptor);
             AddGas(descriptor.FixedPrice);
             List<object> parameters = descriptor.Parameters.Count > 0
                 ? new List<object>()