diff --git a/Doxyfile.in b/Doxyfile.in
index 5bb0916..2288465 100644
--- a/Doxyfile.in
+++ b/Doxyfile.in
@@ -506,7 +506,7 @@
 # will be excluded. Set it to YES to include the internal documentation.
 # The default value is: NO.
 
-INTERNAL_DOCS          = NO
+INTERNAL_DOCS          = @INTERNAL_DOCS@
 
 # If the CASE_SENSE_NAMES tag is set to NO then doxygen will only generate file
 # names in lower-case letters. If set to YES, upper-case letters are also