diff --git a/src/fileio_type.h b/src/fileio_type.h
index c871c1c14b..a353e12b8a 100644
--- a/src/fileio_type.h
+++ b/src/fileio_type.h
@@ -40,6 +40,8 @@ enum DetailedFileType {
 	DFT_FIOS_DIR,    ///< A directory entry.
 	DFT_FIOS_DIRECT, ///< Direct filename.
 
+	DFT_END,         ///< End of this enum. Supports a compile time size check against _fios_colours in fios_gui.cpp
+
 	DFT_INVALID = 255, ///< Unknown or invalid file.
 };
 
diff --git a/src/fios_gui.cpp b/src/fios_gui.cpp
index bea51f9851..993d331a55 100644
--- a/src/fios_gui.cpp
+++ b/src/fios_gui.cpp
@@ -238,7 +238,8 @@ static const TextColour _fios_colours[] = {
 	TC_DARK_GREEN,   // DFT_FIOS_DIR
 	TC_ORANGE,       // DFT_FIOS_DIRECT
 };
-
+/* This should align with the DetailedFileType enum defined in fileio_type.h */
+static_assert(std::size(_fios_colours) == DFT_END);
 
 /**
  * Sort the collected list save games prior to displaying it in the save/load gui.