diff --git a/macq/extract/slaf.py b/macq/extract/slaf.py
index c8060b5c..f671865d 100644
--- a/macq/extract/slaf.py
+++ b/macq/extract/slaf.py
@@ -197,7 +197,9 @@ def __sort_results(observations: ObservedTraceList, entailed: Set):
                 precond = info_split[0]
                 action = info_split[1]
                 # update the precondition of this action with the appropriate fluent
-                learned_actions[action].update_precond({precond})
+                #  only if it's a positive precondition
+                if "~" not in precond:
+                    learned_actions[action].update_precond({precond})
             # if this proposition holds information about an effect
             elif effect in e:
                 # split to separate effect and action, get rid of extra brackets