diff --git a/src/common/filesystem/include/resourcefile.h b/src/common/filesystem/include/resourcefile.h
index 7709822e11..7dea3304bb 100644
--- a/src/common/filesystem/include/resourcefile.h
+++ b/src/common/filesystem/include/resourcefile.h
@@ -107,6 +107,8 @@ struct FResourceEntry
 	int16_t Namespace;
 };
 
+void SetMainThread();
+
 class FResourceFile
 {
 public:
diff --git a/src/common/filesystem/source/filesystem.cpp b/src/common/filesystem/source/filesystem.cpp
index 86029186e1..e2be0b1870 100644
--- a/src/common/filesystem/source/filesystem.cpp
+++ b/src/common/filesystem/source/filesystem.cpp
@@ -245,6 +245,8 @@ bool FileSystem::InitMultipleFiles (std::vector<std::string>& filenames, LumpFil
 {
 	int numfiles;
 
+	// the first call here will designate a main thread which may use shared file readers. All other thewads have to open new file handles.
+	SetMainThread();
 	// open all the files, load headers, and count lumps
 	DeleteAll();
 	numfiles = 0;
diff --git a/src/common/filesystem/source/resourcefile.cpp b/src/common/filesystem/source/resourcefile.cpp
index 3a64cf13b6..1933c59aae 100644
--- a/src/common/filesystem/source/resourcefile.cpp
+++ b/src/common/filesystem/source/resourcefile.cpp
@@ -45,6 +45,18 @@
 
 namespace FileSys {
 	
+// this is for restricting shared file readers to the main thread.
+thread_local bool mainThread;
+void SetMainThread()
+{
+	// only set the global flag on the first thread calling this.
+	static bool done = false;
+	if (!done)
+	{
+		mainThread = done = true;
+	}
+}
+
 std::string ExtractBaseName(const char* path, bool include_extension)
 {
 	const char* src, * dot;
@@ -553,6 +565,8 @@ FileReader FResourceFile::GetEntryReader(uint32_t entry, int readertype, int rea
 		}
 		if (!(Entries[entry].Flags & RESFF_COMPRESSED))
 		{
+			if (readertype == READER_SHARED && mainThread)
+				readertype = READER_NEW;
 			if (readertype == READER_SHARED)
 			{
 				fr.OpenFilePart(Reader, Entries[entry].Position, Entries[entry].Length);
@@ -571,7 +585,7 @@ FileReader FResourceFile::GetEntryReader(uint32_t entry, int readertype, int rea
 		else
 		{
 			FileReader fri;
-			if (readertype == READER_NEW) fri.OpenFile(FileName, Entries[entry].Position, Entries[entry].CompressedSize);
+			if (readertype == READER_NEW || !mainThread) fri.OpenFile(FileName, Entries[entry].Position, Entries[entry].CompressedSize);
 			else fri.OpenFilePart(Reader, Entries[entry].Position, Entries[entry].CompressedSize);
 			int flags = DCF_TRANSFEROWNER | DCF_EXCEPTIONS;
 			if (readertype == READER_CACHED) flags |= DCF_CACHED;