diff --git a/src/resourcefiles/resourcefile.cpp b/src/resourcefiles/resourcefile.cpp
index 96bd50e0f5..18a6b6f15b 100644
--- a/src/resourcefiles/resourcefile.cpp
+++ b/src/resourcefiles/resourcefile.cpp
@@ -716,3 +716,24 @@ int FExternalLump::FillCache()
 	return 1;
 }
 
+
+bool FMemoryFile::Open(bool quiet)
+{
+    FString name(ExtractFileBase(Filename));
+    FString fname(ExtractFileBase(Filename, true));
+    
+    Lumps = new FUncompressedLump[1];    // must use array allocator
+    uppercopy(Lumps->Name, name);
+    Lumps->Name[8] = 0;
+    Lumps->FullName = fname;
+    Lumps->Owner = this;
+    Lumps->Position = 0;
+    Lumps->LumpSize = Reader->GetLength();
+    Lumps->Namespace = ns_global;
+    Lumps->Flags = 0;
+    Lumps->FullName = NULL;
+    NumLumps = 1;
+    return true;
+}
+
+
diff --git a/src/resourcefiles/resourcefile.h b/src/resourcefiles/resourcefile.h
index 4cc93cd2eb..f7cc806e2b 100644
--- a/src/resourcefiles/resourcefile.h
+++ b/src/resourcefiles/resourcefile.h
@@ -160,24 +160,7 @@ struct FMemoryFile : public FUncompressedFile
 		Reader = &mr;
 	}
 
-	bool Open(bool quiet)
-	{
-		FString name(ExtractFileBase(Filename));
-		FString fname(ExtractFileBase(Filename, true));
-
-		Lumps = new FUncompressedLump[1];	// must use array allocator
-		uppercopy(Lumps->Name, name);
-		Lumps->Name[8] = 0;
-		Lumps->FullName = fname;
-		Lumps->Owner = this;
-		Lumps->Position = 0;
-		Lumps->LumpSize = Reader->GetLength();
-		Lumps->Namespace = ns_global;
-		Lumps->Flags = 0;
-		Lumps->FullName = NULL;
-		NumLumps = 1;
-		return true;
-	}
+    bool Open(bool quiet);
 
 
 };
@@ -185,4 +168,4 @@ struct FMemoryFile : public FUncompressedFile
 
 
 
-#endif
\ No newline at end of file
+#endif