diff --git a/tools/check-java-versions.sh b/tools/check-java-versions.sh
new file mode 100755
index 0000000..5058c3c
--- /dev/null
+++ b/tools/check-java-versions.sh
@@ -0,0 +1,16 @@
+#!/bin/bash
+
+TMP=$(mktemp --directory)
+
+pushd build
+  for JAR in $(find . -name "*.jar" -a -not -name "*-sources.jar" -a -not -name "*-javadoc.jar")
+  do
+    echo "Checking ${JAR}..."
+    unzip -qq -d ${TMP} ${JAR}
+    find ${TMP} -name "*.class" | xargs file -b | sort -u
+    rm -rf ${TMP}/*
+    echo
+  done
+popd
+
+rm -rf ${TMP}
diff --git a/tools/retrolambda-2.5.6.jar b/tools/retrolambda-2.5.6.jar
new file mode 100644
index 0000000..2c7a740
Binary files /dev/null and b/tools/retrolambda-2.5.6.jar differ
diff --git a/tools/retrolambda.sh b/tools/retrolambda.sh
new file mode 100755
index 0000000..aac7883
--- /dev/null
+++ b/tools/retrolambda.sh
@@ -0,0 +1,40 @@
+#!/bin/sh
+
+set -x
+
+if [ $# -ne 1 ]
+then
+    echo Provide on jar file to convert on the command line.
+    exit 1
+fi
+
+REALPATH=$(realpath $0)
+BIN_DIR=`dirname "$REALPATH"`
+LIB_DIR=$BIN_DIR
+
+JAR_TO_CONVERT="$1"
+INPUT_DIR="$JAR_TO_CONVERT".inputdir
+OUTPUT_DIR="$JAR_TO_CONVERT".outputdir
+
+rm -rf "$INPUT_DIR"
+rm -rf "$OUTPUT_DIR"
+mkdir "$INPUT_DIR"
+mkdir "$OUTPUT_DIR"
+(cd "$INPUT_DIR"; jar -xvf $OLDPWD/"$JAR_TO_CONVERT")
+
+java \
+    -Dretrolambda.bytecodeVersion=49          \
+    -Dretrolambda.defaultMethods=true         \
+    -Dretrolambda.inputDir="$INPUT_DIR"       \
+    -Dretrolambda.outputDir="$OUTPUT_DIR"     \
+    -Dretrolambda.classpath="$JAR_TO_CONVERT" \
+    -Dretrolambda.javacHacks=true             \
+    -Dretrolambda.quiet=false                 \
+    -jar "$LIB_DIR"/retrolambda-2.5.6.jar
+
+# The order of the "m" and "f" must match the order that the
+# corresponding files appear in the argument list. This is
+# so stupid...
+jar -cvfm "$JAR_TO_CONVERT".java5.jar \
+    "$OUTPUT_DIR"/META-INF/MANIFEST.MF \
+    -C "$OUTPUT_DIR" .