diff --git a/rpcs3/Emu/Cell/lv2/sys_fs.cpp b/rpcs3/Emu/Cell/lv2/sys_fs.cpp
index 5feb0237ab..1eaf0a1980 100644
--- a/rpcs3/Emu/Cell/lv2/sys_fs.cpp
+++ b/rpcs3/Emu/Cell/lv2/sys_fs.cpp
@@ -257,8 +257,15 @@ error_code sys_fs_open(vm::cptr<char> path, s32 flags, vm::ptr<u32> fd, s32 mode
 		}
 	}
 
-	if (flags & ~(CELL_FS_O_ACCMODE | CELL_FS_O_CREAT | CELL_FS_O_TRUNC | CELL_FS_O_APPEND | CELL_FS_O_EXCL | CELL_FS_O_MSELF))
+	if (flags & CELL_FS_O_UNK)
 	{
+		sys_fs.warning("sys_fs_open called with CELL_FS_O_UNK flag enabled. FLAGS: %#o", flags);
+	}
+
+	// Tests have shown that invalid combinations get resolved internally (without exceptions), but that would complicate code with minimal accuracy gains.
+	// For example, no games are known to try and call TRUNCATE | APPEND | RW, or APPEND | READ, which currently would cause an exception.
+	if (flags & ~(CELL_FS_O_UNK | CELL_FS_O_ACCMODE | CELL_FS_O_CREAT | CELL_FS_O_TRUNC | CELL_FS_O_APPEND | CELL_FS_O_EXCL | CELL_FS_O_MSELF))
+	{ 
 		open_mode = {}; // error
 	}
 
diff --git a/rpcs3/Emu/Cell/lv2/sys_fs.h b/rpcs3/Emu/Cell/lv2/sys_fs.h
index 4ab07f63aa..48f26cb23d 100644
--- a/rpcs3/Emu/Cell/lv2/sys_fs.h
+++ b/rpcs3/Emu/Cell/lv2/sys_fs.h
@@ -15,6 +15,7 @@ enum : s32
 	CELL_FS_O_TRUNC   = 001000,
 	CELL_FS_O_APPEND  = 002000,
 	CELL_FS_O_MSELF   = 010000,
+	CELL_FS_O_UNK     = 01000000, // Tests have shown this is independent of other flags.  Only known to be called in Rockband games.
 };
 
 // Seek Mode