diff --git a/scripts/grt/export.py b/scripts/grt/export.py
index 24e5f447ce0..a3eab5d71ce 100644
--- a/scripts/grt/export.py
+++ b/scripts/grt/export.py
@@ -49,7 +49,10 @@ def kw_metrics(job):
 
 
 def round_to_2sd(number):
-    return str(int(float('%.2g' % number)))
+    if number:
+        return str(int(float('%.2g' % number)))
+    else:
+        return '-1'
 
 
 def main(argv):