diff --git a/contrib/ChangeLog b/contrib/ChangeLog
index 4493c19dfd175f3d59e8879c8cb1bad2b45874a1..cfd3abbf3f2447fdcc019432e0972b357cdb2fee 100644
--- a/contrib/ChangeLog
+++ b/contrib/ChangeLog
@@ -1,3 +1,8 @@
+2015-09-11  Markus Trippelsdorf  <markus@trippelsdorf.de>
+
+	* download_prerequisites: Make sure that script is run from
+	top level source directory.
+
 2015-08-27  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
 	* update-copyright.py (GCCCmdLine): Add libvtv.
diff --git a/contrib/download_prerequisites b/contrib/download_prerequisites
index de0e7c41847d9cd95aae55a1bcceed13203484f0..69403301b813a2b99975570145078d5d88deb3fb 100755
--- a/contrib/download_prerequisites
+++ b/contrib/download_prerequisites
@@ -24,6 +24,11 @@
 # be downloaded.
 GRAPHITE_LOOP_OPT=yes
 
+if [ ! -e gcc/BASE-VER ] ; then
+	echo "You must run this script in the top level GCC source directory."
+	exit 1
+fi
+
 # Necessary to build GCC.
 MPFR=mpfr-2.4.2
 GMP=gmp-4.3.2