diff --git a/docs/ase-file-specs.md b/docs/ase-file-specs.md
index e2285598e..183f07b81 100644
--- a/docs/ase-file-specs.md
+++ b/docs/ase-file-specs.md
@@ -277,7 +277,6 @@ reference external palettes, tilesets, or extensions that make use of extended p
                   2 - Extension name for properties
       BYTE[7]   Reserved (set to zero)
       STRING    External file name or extension ID
-                When this is an extension ID, it starts with the prefix "extension:"
 
 ### Mask Chunk (0x2016) DEPRECATED