diff --git a/src/Horus/Preprocessor.hs b/src/Horus/Preprocessor.hs
index 71709c7d..7c300957 100644
--- a/src/Horus/Preprocessor.hs
+++ b/src/Horus/Preprocessor.hs
@@ -163,15 +163,22 @@ instance Show Model where
 
 solve :: Integer -> Text -> PreprocessorL SolverResult
 solve fPrime smtQuery = do
-  optimizeQuery smtQuery >>= foldlM combineResult (Unknown Nothing)
+  combinedRes <- optimizeQuery smtQuery >>= foldlM combineResult (False, Unsat)
+  pure $ case combinedRes of
+    (_, Sat mbModel) -> Sat mbModel
+    (_, Unknown mbReason) -> Unknown mbReason
+    (True, Unsat) -> Unknown $ Just "All solvers failed on at least one goal."
+    (False, Unsat) -> Unsat
  where
-  combineResult (Sat mbModel) _ = pure (Sat mbModel)
-  combineResult Unsat subgoal = do
-    result <- computeResult subgoal
-    pure $ case result of
-      Sat mbModel -> Sat mbModel
-      _ -> Unsat
-  combineResult Unknown{} subgoal = computeResult subgoal
+  combineResult :: (Bool, SolverResult) -> Goal -> PreprocessorL (Bool, SolverResult)
+  -- The combined value (Bool, SolverResult) means (was there an unknown, SolverResult so far)
+  combineResult (hadUnknown, Sat mbModel) _ = pure (hadUnknown, Sat mbModel)
+  combineResult (hadUnknown, Unsat) subgoal = do
+    res <- computeResult subgoal
+    pure (hadUnknown, res)
+  combineResult (_, Unknown{}) subgoal = do
+    res <- computeResult subgoal
+    pure (True, res)
 
   computeResult subgoal = do
     result <- runSolver =<< runZ3 (goalToSExpr subgoal)