diff --git a/configure.ac b/configure.ac
index 9477dbb7..8fb5317b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -215,6 +215,8 @@ AM_PROG_AS
 AC_USE_SYSTEM_EXTENSIONS
 AC_C_VARARRAYS
 
+AC_CHECK_DEFINE([__wasi__], [WASI="yes"], [])
+
 AC_CHECK_DEFINE([_FORTIFY_SOURCE], [], [
   AX_CHECK_COMPILE_FLAG([-D_FORTIFY_SOURCE=2],
     [CPPFLAGS="$CPPFLAGS -D_FORTIFY_SOURCE=2"])
diff --git a/dist-build/wasi.sh b/dist-build/wasi.sh
index 15ba4469..00a72cd1 100755
--- a/dist-build/wasi.sh
+++ b/dist-build/wasi.sh
@@ -20,6 +20,9 @@ export STRIP="llvm-strip"
 
 make distclean > /dev/null
 
+egrep -q -F -- '-wasi' build-aux/config.sub || \
+  sed -i -e 's/-nacl\*)/-nacl*|-wasi/' build-aux/config.sub
+
 if [ -z "$LIBSODIUM_FULL_BUILD" ]; then
   export LIBSODIUM_ENABLE_MINIMAL_FLAG="--enable-minimal"
 else