diff -u -r ../cln-1.3.4/src/base/low/cl_low_mul.cc ./src/base/low/cl_low_mul.cc
--- ../cln-1.3.4/src/base/low/cl_low_mul.cc	2011-04-08 23:06:30.000000000 +0200
+++ ./src/base/low/cl_low_mul.cc	2017-01-15 18:42:11.755489083 +0100
@@ -50,11 +50,11 @@
 
 
 #ifdef NEED_VAR_mulu64_high
-uint64 mulu64_high;
+extern "C" uint64 mulu64_high;
 #endif
 
 #ifdef NEED_FUNCTION_mulu64_
-uint64 mulu64_high;
+extern "C" uint64 mulu64_high;
 namespace cln {
 extern "C" uint64 mulu64_ (uint64 x, uint64 y);
 uint64 mulu64_ (uint64 x, uint64 y)