diff --git a/robotlab_safety/pluto_auto.py b/robotlab_safety/pluto_auto.py
index 1c509d05816023fa95a08cff5f2829f4702b21da..8625d437b8edcf94adcda1c316594f154b19442c 100755
--- a/robotlab_safety/pluto_auto.py
+++ b/robotlab_safety/pluto_auto.py
@@ -31,7 +31,9 @@ class PlutoVariables:
                     rh.append(expr.format(*matches, pluto=v[0]))
                     pass
                 pass
-            if op == 'AND':
+            if len(rh) == 0:
+                return("%s=0" % (lh))
+            elif op == 'AND':
                 return("%s=%s" % (lh, '*'.join(rh)))
             elif op == 'OR':
                 return("%s=%s" % (lh, '+'.join(rh)))