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--- a/Makefile.am
+++ b/Makefile.am
@@ -109,7 +109,9 @@
     libupnpp/upnpputils.hxx \
     libupnpp/workqueue.h
 
-libupnpp_la_LDFLAGS = -version-info $(VERSION_INFO)
+# Curiously, -no-undefined seems to do nothing?? -Wl,-zdefs works though.
+# automake 1.14.1
+libupnpp_la_LDFLAGS = -Wl,-zdefs -no-undefined -version-info $(VERSION_INFO)
 
 libupnpp_la_LIBADD = $(LIBUPNPP_LIBS)