diff -r b6601923cf1f -r 717e96cf9527 src/Pure/Thy/latex.ML
--- a/src/Pure/Thy/latex.ML	Fri Jul 08 16:01:14 2011 +0200
+++ b/src/Pure/Thy/latex.ML	Fri Jul 08 16:13:34 2011 +0200
@@ -83,6 +83,7 @@
     ("~", "{\\isachartilde}")];
 
 fun output_chr " " = "\\ "
+  | output_chr "\t" = "\\ "
   | output_chr "\n" = "\\isanewline\n"
   | output_chr c =
       (case Symtab.lookup char_table c of