diff --git a/doc/doxygen.cfg b/doc/doxygen.cfg
index a2c4fd07..4a022de1 100644
--- a/doc/doxygen.cfg
+++ b/doc/doxygen.cfg
@@ -27,7 +27,6 @@ INHERIT_DOCS           = YES
 SEPARATE_MEMBER_PAGES  = NO
 TAB_SIZE               = 8
 ALIASES                =
-TCL_SUBST              =
 OPTIMIZE_OUTPUT_FOR_C  = YES
 OPTIMIZE_OUTPUT_JAVA   = NO
 OPTIMIZE_FOR_FORTRAN   = NO