diff --git a/Source/Engine/Tools/MaterialGenerator/MaterialGenerator.Material.cpp b/Source/Engine/Tools/MaterialGenerator/MaterialGenerator.Material.cpp
index c778c03ee..bdade721e 100644
--- a/Source/Engine/Tools/MaterialGenerator/MaterialGenerator.Material.cpp
+++ b/Source/Engine/Tools/MaterialGenerator/MaterialGenerator.Material.cpp
@@ -790,9 +790,21 @@ void MaterialGenerator::ProcessGroupFunction(Box* box, Node* node, Value& value)
     // Function Input
     case 1:
     {
+        // Check the stack count.If only 1 graph is present,
+        // we are processing the graph in isolation (e.g., in the Editor Preview).
+        // In this case, we skip the caller-finding logic and use the node's default value.
+        if (_graphStack.Count() < 2)
+        {
+            // Use the default value from the function input node's box (usually box 1)
+            value = tryGetValue(node->TryGetBox(1), Value::Zero);
+            break;
+        }
+
         // Find the function call
         Node* functionCallNode = nullptr;
-        ASSERT(_graphStack.Count() >= 2);
+        
+        // The original ASSERT has been effectively replaced by the 'if' above.
+        //ASSERT(_graphStack.Count() >= 2);
         Graph* graph;
         for (int32 i = _callStack.Count() - 1; i >= 0; i--)
         {