diff --git a/build.sh b/build.sh
index 77766cf..73ac773 100755
--- a/build.sh
+++ b/build.sh
@@ -10,7 +10,7 @@ DIR=$(pwd)
 # The latest required version of Wattsi. Update this and the fallback in
 # https://github.com/whatwg/wattsi/blob/master/src/build.sh if you change how ./build.sh invokes
 # Wattsi.
-WATTSI_LATEST=83
+WATTSI_LATEST=84
 
 # Shared state variables throughout this script
 LOCAL_WATTSI=true