diff --git a/doc/acrn.doxyfile b/doc/acrn.doxyfile
index 4af6dcf61..fddfed5b7 100644
--- a/doc/acrn.doxyfile
+++ b/doc/acrn.doxyfile
@@ -2169,7 +2169,7 @@ EXTERNAL_PAGES         = YES
 # interpreter (i.e. the result of 'which perl').
 # The default file (with absolute path) is: /usr/bin/perl.
 
-PERL_PATH              = /usr/bin/perl
+# obsolete with 1.8.17 PERL_PATH              = /usr/bin/perl
 
 #---------------------------------------------------------------------------
 # Configuration options related to the dot tool
@@ -2191,7 +2191,7 @@ CLASS_DIAGRAMS         = YES
 # the mscgen tool resides. If left empty the tool is assumed to be found in the
 # default search path.
 
-MSCGEN_PATH            =
+# obsolete with 1.8.17 MSCGEN_PATH            =
 
 # You can include diagrams made with dia in doxygen documentation. Doxygen will
 # then run dia to produce the diagram and insert it in the documentation. The