diff --git a/lib/browser/build b/lib/browser/build
--- a/lib/browser/build
+++ b/lib/browser/build
@@ -1,72 +1,72 @@
 #!/usr/bin/env bash
 #
 # Author: Makarius
 #
 # mk - build graph browser
 #
 # Requires proper Isabelle settings environment.
 
 
 ## diagnostics
 
 function fail()
 {
   echo "$1" >&2
   exit 2
 }
 
 [ -n "$ISABELLE_HOME" ] || fail "Missing Isabelle settings environment"
 
 
 ## dependencies
 
 declare -a SOURCES=(
   GraphBrowser/AWTFontMetrics.java
   GraphBrowser/AbstractFontMetrics.java
   GraphBrowser/Box.java
   GraphBrowser/Console.java
   GraphBrowser/DefaultFontMetrics.java
   GraphBrowser/Directory.java
   GraphBrowser/DummyVertex.java
   GraphBrowser/Graph.java
   GraphBrowser/GraphBrowser.java
   GraphBrowser/GraphBrowserFrame.java
   GraphBrowser/GraphView.java
   GraphBrowser/NormalVertex.java
   GraphBrowser/ParseError.java
   GraphBrowser/Region.java
   GraphBrowser/Spline.java
   GraphBrowser/TreeBrowser.java
   GraphBrowser/TreeNode.java
   GraphBrowser/Vertex.java
   awtUtilities/Border.java
   awtUtilities/MessageDialog.java
   awtUtilities/TextFrame.java
 )
 
 TARGET="$ISABELLE_HOME/lib/browser/GraphBrowser.jar"
 
 
 ## main
 
 OUTDATED=false
 
 for SOURCE in "${SOURCES[@]}"
 do
   [ ! -e "$SOURCE" ] && fail "Missing source file: $SOURCE"
   [ ! -e "$TARGET" -o "$SOURCE" -nt "$TARGET" ] && OUTDATED=true
 done
 
 if [ "$OUTDATED" = true ]
 then
   echo >&2 "### Building graph browser ..."
 
   rm -rf classes && mkdir classes
 
-  isabelle_jdk javac -d classes -source 7 "${SOURCES[@]}" || \
+  isabelle_jdk javac -d classes -Xlint:-options -source 7 -target 7 "${SOURCES[@]}" || \
     fail "Failed to compile sources"
   isabelle_jdk jar cf "$(platform_path "$TARGET")" -C classes . ||
     fail "Failed to produce $TARGET"
 
   rm -rf classes
 fi