diff --git a/attic/world/build.sh b/attic/world/build.sh
index d8800cd4c..f3bcfabc9 100755
--- a/attic/world/build.sh
+++ b/attic/world/build.sh
@@ -1,3 +1,3 @@
 #!/bin/bash
 
-c++ -std=c++11 -I../.. -I.. -g -o mkworld ../../node/C25519.cpp ../../node/Salsa20.cpp ../../node/SHA512.cpp ../../node/Identity.cpp ../../node/Utils.cpp ../../node/InetAddress.cpp ../../osdep/OSUtils.cpp mkworld.cpp -lm
+c++ -std=c++11 -I../.. -I../../ext -I.. -g -o mkworld ../../node/C25519.cpp ../../node/Salsa20.cpp ../../node/SHA512.cpp ../../node/Identity.cpp ../../node/Utils.cpp ../../node/InetAddress.cpp ../../osdep/OSUtils.cpp mkworld.cpp -lm