diff --git a/regen_build_ninja_in.sh b/regen_build_ninja_in.sh
new file mode 100755
index 0000000..152fd95
--- /dev/null
+++ b/regen_build_ninja_in.sh
@@ -0,0 +1,32 @@
+#!/bin/bash
+
+SRC=$(cd $(dirname $0) && pwd)
+OUT=/tmp/blueprint.$$
+
+rm -rf ${OUT}
+mkdir ${OUT}
+
+(
+  cd ${OUT}
+  ${SRC}/bootstrap.bash
+  ./blueprint.bash
+  ${SRC}/bootstrap.bash -r
+)
+
+rm -rf ${OUT}
+mkdir ${OUT}
+
+(
+  cd ${OUT}
+  cp -r ${SRC}/tests/test_tree test_tree
+  ln -s ${SRC} test_tree/blueprint
+  mkdir out
+  cd out
+
+  export SRCDIR=../test_tree
+  ${SRCDIR}/blueprint/bootstrap.bash
+  ./blueprint.bash
+  cp .minibootstrap/build.ninja.in ${SRC}/tests/test_tree/build.ninja.in
+)
+
+rm -rf ${OUT}
diff --git a/tests/test_tree_tests.sh b/tests/test_tree_tests.sh
index 43f12fc..515e2b6 100755
--- a/tests/test_tree_tests.sh
+++ b/tests/test_tree_tests.sh
@@ -23,6 +23,7 @@
 
 if ! cmp -s ${SRCDIR}/build.ninja.in .minibootstrap/build.ninja.in; then
     echo "tests/test_tree/build.ninja.in and .minibootstrap/build.ninja.in should be the same" >&2
+    echo "run regen_build_ninja_in.sh" >&2
     exit 1
 fi