diff --git a/tests/FILEFORMAT.md b/tests/FILEFORMAT.md
index 263ce7f067..0a0aee0fec 100644
--- a/tests/FILEFORMAT.md
+++ b/tests/FILEFORMAT.md
@@ -55,9 +55,11 @@ To insert a sequence of bytes from a hex encoded string, use this syntax:
 
     %hex[ %XX-encoded data to decode ]hex%
 
+Other bytes within the brackets that not percent encoded are inserted as-is.
+
 For example, to insert the binary octets 0, 1 and 255 into the test file:
 
-    %hex[ %00%01%FF ]hex%
+    %hex[%00%01%FF]hex%
 
 ## Repeat content