diff --git a/local/scripts/check-prefix-freshness.sh b/local/scripts/check-prefix-freshness.sh
new file mode 100755
index 0000000000..b0c6b45da7
--- /dev/null
+++ b/local/scripts/check-prefix-freshness.sh
@@ -0,0 +1,93 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+project_root="$(git -C "$script_dir" rev-parse --show-toplevel)"
+
+if [[ -t 1 ]]; then
+    c_reset=$'\033[0m'
+    c_red=$'\033[31m'
+    c_green=$'\033[32m'
+    c_yellow=$'\033[33m'
+else
+    c_reset=''
+    c_red=''
+    c_green=''
+    c_yellow=''
+fi
+
+ok() { printf '%sOK%s: %s\n' "$c_green" "$c_reset" "$*"; }
+warn() { printf '%sWARN%s: %s\n' "$c_yellow" "$c_reset" "$*"; }
+fail() { printf '%sFAIL%s: %s\n' "$c_red" "$c_reset" "$*" >&2; }
+
+usage() {
+    cat <<EOF
+Usage: $(basename "$0") [--doctor] [--simulate-staleness]
+
+Check whether the compiled prefix libc.a is older than local fork commits.
+
+Options:
+  --doctor              Print verbose component/file diagnostics
+  --simulate-staleness   Force an artificial stale-prefix result for testing
+  -h, --help            Show this help
+EOF
+}
+
+doctor=0
+simulate_staleness=0
+for arg in "$@"; do
+    case "$arg" in
+        --doctor) doctor=1 ;;
+        --simulate-staleness) simulate_staleness=1 ;;
+        -h|--help) usage; exit 0 ;;
+        *) fail "unknown argument: $arg"; usage; exit 2 ;;
+    esac
+done
+
+latest_prefix_mtime() {
+    local latest=0 path ts
+    for path in \
+        "$project_root/prefix/x86_64-unknown-redox/sysroot/x86_64-unknown-redox/lib/libc.a" \
+        "$project_root/prefix/x86_64-unknown-redox/relibc-install/x86_64-unknown-redox/lib/libc.a"; do
+        if [[ -e "$path" ]]; then
+            ts=$(stat -c %Y "$path")
+            (( ts > latest )) && latest=$ts
+        fi
+    done
+    printf '%s' "$latest"
+}
+
+fork_mtime() {
+    local path="$1"
+    git -C "$project_root" log -1 --format=%ct -- "$path" 2>/dev/null || printf '0'
+}
+
+components=(relibc kernel base)
+stale=0
+prefix_ts="$(latest_prefix_mtime)"
+
+if (( simulate_staleness )); then
+    prefix_ts=0
+fi
+
+for component in "${components[@]}"; do
+    path="local/sources/$component"
+    fork_ts="$(fork_mtime "$path")"
+    delta=$((fork_ts - prefix_ts))
+    if (( doctor )); then
+        printf '%s: fork=%s prefix=%s delta=%s\n' "$path" "$fork_ts" "$prefix_ts" "$delta"
+    fi
+    if (( fork_ts > prefix_ts )); then
+        printf '%s: lib too old by %s seconds\n' "$component" "$delta"
+        stale=1
+    else
+        ok "$component: prefix fresh"
+    fi
+done
+
+if (( stale )); then
+    warn "prefix is stale — run ./local/scripts/build-redbear.sh --upstream"
+    exit 1
+fi
+
+ok "prefix is fresh"