diff --git a/documentation/Doxyfile.in b/documentation/Doxyfile.in
index f4044661b..09fa968e2 100644
--- a/documentation/Doxyfile.in
+++ b/documentation/Doxyfile.in
@@ -1243,6 +1243,7 @@ INCLUDE_FILE_PATTERNS  =
 # instead of the = operator.
 
 PREDEFINED             = FL_DOXYGEN \
+                         FLTK_ABI_VERSION=99999 \
                          FLTK_HAVE_CAIRO \
                          HAVE_GL \
                          HAVE_GL_OVERLAY \