diff --git a/thys/Sturm_Sequences/ROOT b/thys/Sturm_Sequences/ROOT
--- a/thys/Sturm_Sequences/ROOT
+++ b/thys/Sturm_Sequences/ROOT
@@ -1,22 +1,22 @@
 chapter AFP
 
 session Sturm_Sequences (AFP) = "HOL-Computational_Algebra" +
-  options [timeout = 600, document_logo = "_",
+  options [timeout = 600, document_logo,
     document_variants = "document:outline=/proof,/ML:userguide"]
   sessions
     "Pure-ex"
   directories
     "Lib"
     "Examples"
   theories
     "Lib/Sturm_Library_Document"
     "Lib/Misc_Polynomial"
   theories [document = false]
     "Lib/Sturm_Library"
   theories
     Sturm_Theorem
     Sturm_Method
     "Examples/Sturm_Ex"
   document_files
     "root.tex"
     "root_userguide.tex"