diff --git a/bin/setup b/bin/setup
index 8bb60140ce..8fe847b529 100755
--- a/bin/setup
+++ b/bin/setup
@@ -7,7 +7,21 @@ root="$(cd "$(dirname "$0")/.." && pwd)"
 
 env BUNDLE_GEMFILE="$root/Gemfile" bundle install
 for gemfile in $root/packages/npm-packages/*/Gemfile; do
+  # FIXME: This is a workaround for the following issue:
+  # 1. `bundle install` does not support auto-self-upgrade for pre-release bundler versions suffixed with ".dev"
+  # 2. ruby-head-wasm-wasi's component build depends on 2.6.0.dev, which added --target-rbconfig support
+  # 3. If the "bundle" command here is earlier than 2.6.0.dev, "bundle install" does *not* self-upgrade to
+  #    the specified pre-release version, and it overwrites the Gemfile.lock with the earlier command version.
+  # 4. Overwritten Gemfile.lock with the earlier bundler version causes auto-self-downgrade when running
+  #    "bundle install --target-rbconfig" inside "rbwasm build" command, then it fails because the earlier
+  #    bundler version does not support --target-rbconfig.
+  #
+  # Thus, we temporarily discard the Gemfile.lock changes here to prevent the auto-self-downgrade issue.
+  # This workaround should be removed once we drop static Ruby builds from ruby-head-wasm-wasi or
+  # a stable bundler version is released with --target-rbconfig support.
+  cp "$gemfile.lock" "$gemfile.lock.orig"
   env BUNDLE_GEMFILE="$gemfile" bundle install
+  mv "$gemfile.lock.orig" "$gemfile.lock"
 done
 
 # Build vendored jco if Rust toolchain is available and submodule is checked out