diff --git a/documentation/Doxyfile.in b/documentation/Doxyfile.in
index 227c4b6fe..4d4529fd7 100644
--- a/documentation/Doxyfile.in
+++ b/documentation/Doxyfile.in
@@ -1328,7 +1328,8 @@ EXTERNAL_GROUPS        = YES
 # fallback. It is recommended to install and use dot, since it yields more
 # powerful graphs.
 
-CLASS_DIAGRAMS         = YES
+#** obsolete as of Doxygen 1.9.3, using default (YES) anyway
+#** CLASS_DIAGRAMS         = YES
 
 # You can define message sequence charts within doxygen comments using the \msc
 # command. Doxygen will then run the mscgen tool (see
@@ -1486,7 +1487,8 @@ MAX_DOT_GRAPH_DEPTH    = 0
 # enabling this option may lead to badly anti-aliased labels on the edges of
 # a graph (i.e. they become hard to read).
 
-DOT_TRANSPARENT        = NO
+#** obsolete as of Doxygen 1.9.5, using default (NO) anyway
+#** DOT_TRANSPARENT        = NO
 
 # Set the DOT_MULTI_TARGETS tag to YES allow dot to generate multiple output
 # files in one run (i.e. multiple -o and -T options on the command line). This