diff --git a/src/common/filesystem/include/fs_files.h b/src/common/filesystem/include/fs_files.h
index e732824974..c3404a5689 100644
--- a/src/common/filesystem/include/fs_files.h
+++ b/src/common/filesystem/include/fs_files.h
@@ -101,31 +101,6 @@ public:
 	long GetLength () const { return Length; }
 };
 
-class MemoryReader : public FileReaderInterface
-{
-protected:
-	const char * bufptr = nullptr;
-	long FilePos = 0;
-
-	MemoryReader()
-	{}
-
-public:
-	MemoryReader(const char *buffer, long length)
-	{
-		bufptr = buffer;
-		Length = length;
-		FilePos = 0;
-	}
-
-	long Tell() const override;
-	long Seek(long offset, int origin) override;
-	long Read(void *buffer, long len) override;
-	char *Gets(char *strbuf, int len) override;
-	virtual const char *GetBuffer() const override { return bufptr; }
-};
-
-
 struct FResourceLump;
 
 class FileReader
@@ -329,24 +304,6 @@ public:
 	friend class FileSystem;
 };
 
-class DecompressorBase : public FileReaderInterface
-{
-	bool exceptions = false;
-public:
-	// These do not work but need to be defined to satisfy the FileReaderInterface.
-	// They will just error out when called.
-	long Tell() const override;
-	long Seek(long offset, int origin) override;
-	char* Gets(char* strbuf, int len) override;
-	void DecompressionError(const char* error, ...) const;
-	void SetOwnsReader();
-	void EnableExceptions(bool on) { exceptions = on; }
-
-protected:
-	FileReader* File = nullptr;
-	FileReader OwnedFile;
-};
-
 
 class FileWriter
 {
diff --git a/src/common/filesystem/include/fs_filesystem.h b/src/common/filesystem/include/fs_filesystem.h
index e976733143..b559494084 100644
--- a/src/common/filesystem/include/fs_filesystem.h
+++ b/src/common/filesystem/include/fs_filesystem.h
@@ -13,9 +13,6 @@
 
 namespace FileSys {
 	
-class FResourceFile;
-struct FResourceLump;
-
 union LumpShortName
 {
 	char		String[9];
diff --git a/src/common/filesystem/include/resourcefile.h b/src/common/filesystem/include/resourcefile.h
index 91d437d388..f714c79954 100644
--- a/src/common/filesystem/include/resourcefile.h
+++ b/src/common/filesystem/include/resourcefile.h
@@ -197,56 +197,6 @@ public:
 	FResourceLump *FindLump(const char *name);
 };
 
-struct FUncompressedLump : public FResourceLump
-{
-	int				Position;
-
-	virtual FileReader *GetReader();
-	virtual int FillCache() override;
-	virtual int GetFileOffset() { return Position; }
-
-};
-
-
-// Base class for uncompressed resource files (WAD, GRP, PAK and single lumps)
-class FUncompressedFile : public FResourceFile
-{
-protected:
-	TArray<FUncompressedLump> Lumps;
-
-	FUncompressedFile(const char *filename, StringPool* sp);
-	FUncompressedFile(const char *filename, FileReader &r, StringPool* sp);
-	virtual FResourceLump *GetLump(int no) { return ((unsigned)no < NumLumps)? &Lumps[no] : NULL; }
-};
-
-
-// should only be used internally.
-struct FExternalLump : public FResourceLump
-{
-	const char* FileName;
-
-	FExternalLump(const char *_filename, int filesize, StringPool* sp);
-	virtual int FillCache() override;
-
-};
-
-struct FMemoryLump : public FResourceLump
-{
-	FMemoryLump(const void* data, int length)
-	{
-		RefCount = INT_MAX / 2;
-		LumpSize = length;
-		Cache = new char[length];
-		memcpy(Cache, data, length);
-	}
-
-	virtual int FillCache() override
-	{
-		RefCount = INT_MAX / 2; // Make sure it never counts down to 0 by resetting it to something high each time it is used.
-		return 1;
-	}
-};
-
 
 }
 
diff --git a/src/common/filesystem/source/file_grp.cpp b/src/common/filesystem/source/file_grp.cpp
index bd543a5592..b289b121d6 100644
--- a/src/common/filesystem/source/file_grp.cpp
+++ b/src/common/filesystem/source/file_grp.cpp
@@ -33,7 +33,7 @@
 **
 */
 
-#include "resourcefile.h"
+#include "resourcefile_internal.h"
 #include "fs_swap.h"
 
 namespace FileSys {
diff --git a/src/common/filesystem/source/file_lump.cpp b/src/common/filesystem/source/file_lump.cpp
index c9885a1269..ad4406a0f4 100644
--- a/src/common/filesystem/source/file_lump.cpp
+++ b/src/common/filesystem/source/file_lump.cpp
@@ -32,7 +32,7 @@
 **
 */
 
-#include "resourcefile.h"
+#include "resourcefile_internal.h"
 
 namespace FileSys {
 //==========================================================================
diff --git a/src/common/filesystem/source/file_pak.cpp b/src/common/filesystem/source/file_pak.cpp
index c8c039209c..4e3b3ef931 100644
--- a/src/common/filesystem/source/file_pak.cpp
+++ b/src/common/filesystem/source/file_pak.cpp
@@ -32,7 +32,7 @@
 **
 */
 
-#include "resourcefile.h"
+#include "resourcefile_internal.h"
 
 namespace FileSys {
 
diff --git a/src/common/filesystem/source/file_rff.cpp b/src/common/filesystem/source/file_rff.cpp
index edb003810c..1d3cf15bf0 100644
--- a/src/common/filesystem/source/file_rff.cpp
+++ b/src/common/filesystem/source/file_rff.cpp
@@ -33,7 +33,7 @@
 **
 */
 
-#include "resourcefile.h"
+#include "resourcefile_internal.h"
 #include "fs_swap.h"
 
 namespace FileSys {
diff --git a/src/common/filesystem/source/file_ssi.cpp b/src/common/filesystem/source/file_ssi.cpp
index 0e48ef49d7..4b68997f0f 100644
--- a/src/common/filesystem/source/file_ssi.cpp
+++ b/src/common/filesystem/source/file_ssi.cpp
@@ -33,7 +33,7 @@
 **
 */
 
-#include "resourcefile.h"
+#include "resourcefile_internal.h"
 
 namespace FileSys {
 //==========================================================================
diff --git a/src/common/filesystem/source/file_whres.cpp b/src/common/filesystem/source/file_whres.cpp
index 41e418773e..efdfd5d395 100644
--- a/src/common/filesystem/source/file_whres.cpp
+++ b/src/common/filesystem/source/file_whres.cpp
@@ -34,7 +34,7 @@
 **
 */
 
-#include "resourcefile.h"
+#include "resourcefile_internal.h"
 #include "fs_stringpool.h"
 #include "fs_swap.h"
 
diff --git a/src/common/filesystem/source/files.cpp b/src/common/filesystem/source/files.cpp
index 4d92cc25cd..5cb1bd3439 100644
--- a/src/common/filesystem/source/files.cpp
+++ b/src/common/filesystem/source/files.cpp
@@ -34,7 +34,7 @@
 */
 
 #include <string>
-#include "fs_files.h"
+#include "files_internal.h"
 
 namespace FileSys {
 	
diff --git a/src/common/filesystem/source/files_decompress.cpp b/src/common/filesystem/source/files_decompress.cpp
index 5948177cf5..86529716a5 100644
--- a/src/common/filesystem/source/files_decompress.cpp
+++ b/src/common/filesystem/source/files_decompress.cpp
@@ -46,6 +46,26 @@
 namespace FileSys {
 	using namespace byteswap;
 
+
+class DecompressorBase : public FileReaderInterface
+{
+	bool exceptions = false;
+public:
+	// These do not work but need to be defined to satisfy the FileReaderInterface.
+	// They will just error out when called.
+	long Tell() const override;
+	long Seek(long offset, int origin) override;
+	char* Gets(char* strbuf, int len) override;
+	void DecompressionError(const char* error, ...) const;
+	void SetOwnsReader();
+	void EnableExceptions(bool on) { exceptions = on; }
+
+protected:
+	FileReader* File = nullptr;
+	FileReader OwnedFile;
+};
+
+
 //==========================================================================
 //
 // DecompressionError
diff --git a/src/common/filesystem/source/files_internal.h b/src/common/filesystem/source/files_internal.h
new file mode 100644
index 0000000000..34e73a0701
--- /dev/null
+++ b/src/common/filesystem/source/files_internal.h
@@ -0,0 +1,31 @@
+#pragma once
+
+#include "fs_files.h"
+
+namespace FileSys {
+
+class MemoryReader : public FileReaderInterface
+{
+protected:
+	const char * bufptr = nullptr;
+	long FilePos = 0;
+
+	MemoryReader()
+	{}
+
+public:
+	MemoryReader(const char *buffer, long length)
+	{
+		bufptr = buffer;
+		Length = length;
+		FilePos = 0;
+	}
+
+	long Tell() const override;
+	long Seek(long offset, int origin) override;
+	long Read(void *buffer, long len) override;
+	char *Gets(char *strbuf, int len) override;
+	virtual const char *GetBuffer() const override { return bufptr; }
+};
+
+}
diff --git a/src/common/filesystem/source/filesystem.cpp b/src/common/filesystem/source/filesystem.cpp
index c8623765e1..2344f09cc4 100644
--- a/src/common/filesystem/source/filesystem.cpp
+++ b/src/common/filesystem/source/filesystem.cpp
@@ -41,6 +41,7 @@
 #include <ctype.h>
 #include <string.h>
 
+#include "resourcefile_internal.h"
 #include "fs_filesystem.h"
 #include "fs_findfile.h"
 #include "md5.hpp"
@@ -320,10 +321,21 @@ int FileSystem::AddExternalFile(const char *filename)
 //
 //==========================================================================
 
+struct FMemoryLump : public FResourceLump
+{
+	FMemoryLump(const void* data, int length)
+	{
+		RefCount = -1;
+		LumpSize = length;
+		Cache = new char[length];
+		memcpy(Cache, data, length);
+	}
+};
+
 int FileSystem::AddFromBuffer(const char* name, const char* type, char* data, int size, int id, int flags)
 {
 	std::string fullname = name;
-	fullname += ':';
+	fullname += '.';
 	fullname += type;
 	auto newlump = new FMemoryLump(data, size);
 	newlump->LumpNameSetup(fullname.c_str(), stringpool);
diff --git a/src/common/filesystem/source/resourcefile.cpp b/src/common/filesystem/source/resourcefile.cpp
index 8a17c09a0a..079998df9c 100644
--- a/src/common/filesystem/source/resourcefile.cpp
+++ b/src/common/filesystem/source/resourcefile.cpp
@@ -35,9 +35,10 @@
 */
 
 #include <zlib.h>
-#include "resourcefile.h"
+#include "resourcefile_internal.h"
 #include "md5.hpp"
 #include "fs_stringpool.h"
+#include "files_internal.h"
 
 namespace FileSys {
 	
diff --git a/src/common/filesystem/source/resourcefile_internal.h b/src/common/filesystem/source/resourcefile_internal.h
new file mode 100644
index 0000000000..4371a7460a
--- /dev/null
+++ b/src/common/filesystem/source/resourcefile_internal.h
@@ -0,0 +1,38 @@
+#pragma once
+
+#include "resourcefile.h"
+
+namespace FileSys {
+struct FUncompressedLump : public FResourceLump
+{
+	int				Position;
+
+	virtual FileReader *GetReader();
+	virtual int FillCache() override;
+	virtual int GetFileOffset() { return Position; }
+
+};
+
+// Base class for uncompressed resource files (WAD, GRP, PAK and single lumps)
+class FUncompressedFile : public FResourceFile
+{
+protected:
+	TArray<FUncompressedLump> Lumps;
+
+	FUncompressedFile(const char *filename, StringPool* sp);
+	FUncompressedFile(const char *filename, FileReader &r, StringPool* sp);
+	virtual FResourceLump *GetLump(int no) { return ((unsigned)no < NumLumps)? &Lumps[no] : NULL; }
+};
+
+
+// should only be used internally.
+struct FExternalLump : public FResourceLump
+{
+	const char* FileName;
+
+	FExternalLump(const char *_filename, int filesize, StringPool* sp);
+	virtual int FillCache() override;
+
+};
+
+}
\ No newline at end of file