diff --git a/configure.ac b/configure.ac
index da96b82..6129b0f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -277,6 +277,12 @@ fi
 
 AC_CHECK_PROGS(JAVAC, ecj jikes "gcj -C" javac)
 
+case "$JAVAC" in
+    javac) JAVAC_FLAGS="-source 1.6 -target 1.6" ;;
+    *)     JAVAC_FLAGS="" ;;
+esac
+AC_SUBST(JAVAC_FLAGS)
+
 dnl Checks for libraries.
 
 dnl Prefer libthr to libpthread (for FreeBSD)
diff --git a/src/classlib/gnuclasspath/lib/Makefile.am b/src/classlib/gnuclasspath/lib/Makefile.am
index 5b08e93..85ee0a8 100644
--- a/src/classlib/gnuclasspath/lib/Makefile.am
+++ b/src/classlib/gnuclasspath/lib/Makefile.am
@@ -50,7 +50,7 @@ inst_classes.zip: classes.zip
 
 classes.zip: $(JAVA_FILES)
 	-mkdir classes
-	$(JAVAC) -bootclasspath ${GLIBJ_ZIP} -d classes $(JAVA_FILES)
+	$(JAVAC) $(JAVAC_FLAGS) -bootclasspath ${GLIBJ_ZIP} -d classes $(JAVA_FILES)
 	cd classes && zip -r ../classes.zip .
 	rm -rf classes