--- a/configure.ac
+++ b/configure.ac
@@ -912,7 +912,7 @@
 dnl zlib is needed for language level 3, and libpng
 # we must define ZLIBDIR regardless because png.mak does a -I$(ZLIBDIR)
 # this seems a harmless default
-ZLIBDIR=src
+ZLIBDIR=$includedir
 AUX_SHARED_ZLIB=
 
 if test -d $srcdir/zlib; then