diff --git a/configure.ac b/configure.ac
index 4d66bece..5637e1d7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -233,7 +233,7 @@ if test x"$with_doxygen" != x"no"; then
     with_doxygen=no
   fi
 fi
-AM_CONDITIONAL([HAVE_DOXYGEN], [test -n "$DOXYGEN"])
+AM_CONDITIONAL(HAVE_DOXYGEN, [test x"$with_doxygen" = x"yes"])
 
 # we need a fully expanded version of $libdir
 # without this we get something like
diff --git a/cplusplus/Makefile.am b/cplusplus/Makefile.am
index 259b1245..d80ca8a7 100644
--- a/cplusplus/Makefile.am
+++ b/cplusplus/Makefile.am
@@ -29,8 +29,8 @@ vips-operators.cpp:
 	./gen-operators.py -g cpp >> vips-operators.cpp
 
 if HAVE_DOXYGEN
-
 html_DATA = html
+endif
 
 html: doxygen.stamp
 
@@ -42,10 +42,9 @@ install-htmlDATA:
 	-mkdir -p $(DESTDIR)$(htmldir)
 	-cp -r html $(DESTDIR)$(htmldir)
 
-endif
-
 EXTRA_DIST = \
 	README.md \
 	vips-operators.cpp \
 	Doxyfile.in \
 	gen-operators.py
+