diff --git a/src/d_iwad.cpp b/src/d_iwad.cpp
index 512e1a905..5c0653b23 100644
--- a/src/d_iwad.cpp
+++ b/src/d_iwad.cpp
@@ -581,7 +581,7 @@ int FIWadManager::IdentifyVersion (TArray<FString> &wadfiles, const char *iwad,
 		// scan the list of found IWADs for a matching one for the current PWAD.
 		for (auto &found : mFoundWads)
 		{
-			if (mIWadInfos[found.mInfoIndex].IWadname.CompareNoCase(iwad) == 0 && mIWadInfos[found.mInfoIndex].prio > pickedprio)
+			if (found.mInfoIndex >= 0 && mIWadInfos[found.mInfoIndex].IWadname.CompareNoCase(iwad) == 0 && mIWadInfos[found.mInfoIndex].prio > pickedprio)
 			{
 				picks.Clear();
 				picks.Push(found);