diff --git a/.gitignore b/.gitignore
index 0d03069..8d1573f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -26,3 +26,4 @@
 /CHANGELOG
 /todo.txt
 /lock
+/hash/
diff --git a/build b/build
index 1f6a94e..d1ff9e9 100755
--- a/build
+++ b/build
@@ -95,6 +95,7 @@ build_release()
 	cd "$srcdir" || $err "$vdir: !cd \"$srcdir\""
 	./update trees -f
 	rmgit .
+	x_ rm -Rf hash repo
 	x_ mv src/docs docs
 	) || $err "can't create release files"
 
diff --git a/include/git.sh b/include/git.sh
index 27b79c1..0de4c93 100644
--- a/include/git.sh
+++ b/include/git.sh
@@ -2,7 +2,7 @@
 # Copyright (c) 2020-2021,2023-2024 Leah Rowe <leah@libreboot.org>
 # Copyright (c) 2022 Caleb La Grange <thonkpeasant@protonmail.com>
 
-eval `setvars "" loc url bkup_url subfile mdir subhash subrepo subrepo_bkup \
+eval `setvars "" loc url bkup_url subfile subhash subrepo subrepo_bkup \
     depend subfile_bkup`
 
 fetch_targets()
@@ -69,9 +69,6 @@ git_prep()
 
 prep_submodules()
 {
-	mdir="$PWD/config/submodule/$project"
-	[ -n "$tree" ] && mdir="$mdir/$tree"
-
 	[ -f "$mdir/module.list" ] && while read -r msrcdir; do
 		fetch_submodule "$msrcdir"
 	done < "$mdir/module.list"; return 0
diff --git a/include/rom.sh b/include/rom.sh
index f2bc37f..ae9c605 100644
--- a/include/rom.sh
+++ b/include/rom.sh
@@ -51,6 +51,8 @@ mkvendorfiles()
 check_coreboot_utils()
 {
 	for util in cbfstool ifdtool; do
+		[ "$badhash" = "n" ] || rm -f "elf/$util/$1/$util" || \
+		    $err "!rm badelf elf/$util/$1/$util"
 		e "elf/$util/$1/$util" f && continue
 
 		utilelfdir="elf/$util/$1"
diff --git a/script/trees b/script/trees
index c31152f..23164ee 100755
--- a/script/trees
+++ b/script/trees
@@ -12,7 +12,7 @@ set -u -e
 eval `setvars "" xarch srcdir premake cmakedir xlang mode makeargs elfdir cmd \
     project target target_dir targets xtree _f release bootstrapargs mkhelper \
     autoconfargs listfile autogenargs btype tree rev tree_depend build_depend \
-    defconfig postmake mkhelpercfg dry dest_dir`
+    defconfig postmake mkhelpercfg dry dest_dir mdir badhash`
 
 main()
 {
@@ -116,7 +116,8 @@ handle_defconfig()
 configure_project()
 {
 	eval `setvars "" xarch xlang build_depend autoconfargs xtree postmake \
-	    tree_depend makeargs btype mkhelper bootstrapargs premake release`
+	    tree_depend makeargs btype mkhelper bootstrapargs premake release \
+	    badhash`
 
 	[ -f "$1/target.cfg" ] || btype="auto"
 	[ -f "$datadir/mkhelper.cfg" ] && eval `setcfg "$datadir/mkhelper.cfg"`
@@ -141,6 +142,11 @@ configure_project()
 
 	[ -z "$mode" ] && build_dependencies
 
+	mdir="$PWD/config/submodule/$project"
+	[ -n "$tree" ] && mdir="$mdir/$tree"
+
+	[ -f "CHANGELOG" ] || check_project_hashes
+
 	[ "$mode" = "fetch" ] || x_ ./update trees -f "$project" $target
 	[ "$mode" = "fetch" ] || return 0
 
@@ -158,6 +164,45 @@ build_dependencies()
 	done; return 0
 }
 
+check_project_hashes()
+{
+	x_ mkdir -p hash
+
+	old_pjhash=""
+	[ ! -f "hash/$project$tree" ] || \
+	    read -r old_pjhash < "hash/$project$tree"
+
+	x_ rm -f "$TMPDIR/project.list" "$TMPDIR/project.hash" \
+	    "$TMPDIR/project.tmp"; x_ touch "$TMPDIR/project.tmp"
+	x_ touch "$TMPDIR/project.hash"
+
+	for delcheck in "$datadir" "$configdir/$tree" "$mdir"; do
+		[ -d "$delcheck" ] || continue
+		find "$delcheck" -type f -not -path "*/.git*/*" \
+		    >> "$TMPDIR/project.tmp" || \
+		    $err "!find $delcheck > project.tmp"
+	done
+	sort "$TMPDIR/project.tmp" > "$TMPDIR/project.list" || \
+	    $err "!sort project tmp/list"
+
+	while read -r delcheck; do
+		[ -f "$delcheck" ] || continue
+		sha512sum "$delcheck" | awk '{print $1}' >> \
+		    "$TMPDIR/project.hash" || $err "!findhash $delcheck"
+	done < "$TMPDIR/project.list"
+
+	pjhash="$(sha512sum "$TMPDIR/project.hash" | awk '{print $1}')" || :
+	badhash="y" && [ "$pjhash" = "$old_pjhash" ] && badhash="n"
+	[ -f "hash/$project$tree" ] || badhash="y"
+
+	printf "%s\n" "$pjhash" > "hash/$project$tree" || \
+	    $err "!mk hash/$project$tree"
+
+	[ "$badhash" = "n" ] || rm -Rf "src/$project/$tree" \
+	    "elf/$project/$tree" "elf/$project/$target" || \
+	    $err "!rmproject $project $tree"; :
+}
+
 check_cross_compiler()
 {
 	for _xarch in $xarch; do