What It Means & How to Fix It in UE5
🧠 Why You’re Seeing This Error
This error means that two or more modules are referencing each other in a circular loop, which Unreal’s build system doesn’t allow.
In UE5, this usually happens when:
- Module A depends on Module B, but Module B also depends on Module A
- You’ve added each other to their
PublicDependencyModuleNamesorPrivateDependencyModuleNameslists - You’re using a class or function from one module in another without proper separation of concerns
💥 Example Error Message
Error: Circular dependency on ModuleA.Build.cs detected
🛠️ Common Scenario
// ModuleA.Build.cs
PublicDependencyModuleNames.Add("ModuleB");
// ModuleB.Build.cs
PublicDependencyModuleNames.Add("ModuleA");
Unreal detects the circular link and throws an error.
✅ How to Fix It in UE5 – Step-by-Step
✔️ 1. Remove the Circular Reference
Check both *.Build.cs files and remove the unnecessary dependency.
// If ModuleA only needs one function from ModuleB,
// consider using forward declarations or interfaces instead
✔️ 2. Use Forward Declarations (If Possible)
Avoid needing to include full headers by using forward declarations:
class UMyClass; // ✅ Forward declared
This reduces dependency needs across modules.
✔️ 3. Create a Shared Utility Module
If both modules truly need to share functionality:
- Create a new module (e.g., ModuleCommon or ModuleShared)
- Move shared classes or logic into it
- Reference this shared module from both ModuleA and ModuleB
✔️ 4. Use Interfaces or Events Instead of Hard Coupling
You can often avoid direct references by using:
- Blueprint Interfaces
- C++ Interfaces
- Delegates or Events
These keep modules loosely coupled.
✅ Summary: How to Fix “Circular Dependency on ModuleA.Build.cs Detected” in UE5
| Cause | Fix Option |
|---|---|
| Module A and B reference each other | Remove one dependency if not truly needed |
| Both need shared access | Create a third shared module and link to that |
| Tight coupling of logic | Use interfaces, events, or delegates instead |
