diff --git a/tests/filter_substr.sh b/tests/filter_substr.sh
index bcf29ef44..37ffadbcc 100755
--- a/tests/filter_substr.sh
+++ b/tests/filter_substr.sh
@@ -34,5 +34,19 @@ EOF
 ${tools_dir}/grib_filter - $sample 2>$temp <<EOF
     transient xx = substr("abc", -1, -1);
 EOF
-grep -q "Invalid substring" $temp
+cat $temp
+grep -q "Invalid substring.*start=" $temp
+
+${tools_dir}/grib_filter - $sample 2>$temp <<EOF
+    transient xx = substr("abc", 0, 0);
+EOF
+cat $temp
+grep -q "Invalid substring.*length must be > 0" $temp
+
+${tools_dir}/grib_filter - $sample 2>$temp <<EOF
+    transient xx = substr("abc", 0, 8);
+EOF
+cat $temp
+grep -q "Invalid substring.*start.*length" $temp
+# Clean up
 rm -f $temp