diff -Naur a/src/Makefile.in b/src/Makefile.in
--- a/src/Makefile.in	2014-10-22 13:10:29.000000000 -0700
+++ b/src/Makefile.in	2015-08-17 23:10:49.730533320 -0700
@@ -3624,7 +3624,7 @@
 	rm -f *.loT
 
 @USE_EXTERNAL_PROTOC_TRUE@unittest_proto_middleman: $(protoc_inputs)
-@USE_EXTERNAL_PROTOC_TRUE@	$(PROTOC) -I$(srcdir) --cpp_out=. $^
+@USE_EXTERNAL_PROTOC_TRUE@	$(PROTOC) -I$(srcdir) --cpp_out=. $(addprefix $(srcdir)/,$^)
 @USE_EXTERNAL_PROTOC_TRUE@	touch unittest_proto_middleman
 
 # We have to cd to $(srcdir) before executing protoc because $(protoc_inputs) is