diff --git a/debian/qualify-clang.sh b/debian/qualify-clang.sh
index fdfccb94..2a0a2d31 100755
--- a/debian/qualify-clang.sh
+++ b/debian/qualify-clang.sh
@@ -353,6 +353,8 @@ echo "#include <fenv.h>" > foo.cc
 NBLINES=$(clang++-$VERSION -P -E foo.cc|wc -l)
 if test $NBLINES -lt 100; then
     echo "Error: more than 100 lines should be returned"
+    echo "output:"
+    clang++-$VERSION -P -E foo.cc
     exit 42
 fi