diff --git a/opm/simulators/flow/Main.hpp b/opm/simulators/flow/Main.hpp
index e2a8b8fc81..d44dae0369 100644
--- a/opm/simulators/flow/Main.hpp
+++ b/opm/simulators/flow/Main.hpp
@@ -319,10 +319,26 @@ protected:
                            Opm::compileTimestamp());
             setupTime_ = externalSetupTimer.elapsed();
         }
-        catch (const std::invalid_argument& e)
+        // readDeck() may throw std::runtime_error on parse failure.
+        // These exceptions are synchronized across MPI ranks via comm.min()
+        // inside readDeck(), so cooperative shutdown is safe — returning false
+        // lets Main::~Main() call MPI_Finalize().
+        catch (const std::runtime_error& e)
         {
             if (outputCout_) {
                 std::cerr << "Failed to create valid EclipseState object." << std::endl;
+                std::cerr << e.what() << std::endl;
+            }
+            exitCode = EXIT_FAILURE;
+            return false;
+        }
+        // Other exceptions (e.g., std::bad_alloc, std::invalid_argument)
+        // may not be synchronized across ranks. Use MPI_Abort() to prevent
+        // deadlocks from unsynchronized failures.
+        catch (const std::exception& e)
+        {
+            if (outputCout_) {
+                std::cerr << "Unexpected error during initialization." << std::endl;
                 std::cerr << "Exception caught: " << e.what() << std::endl;
             }
 #if HAVE_MPI
diff --git a/opm/simulators/utils/readDeck.cpp b/opm/simulators/utils/readDeck.cpp
index 33a5b997e0..345c917648 100644
--- a/opm/simulators/utils/readDeck.cpp
+++ b/opm/simulators/utils/readDeck.cpp
@@ -780,6 +780,10 @@ void Opm::readDeck(Opm::Parallel::Communication    comm,
         errorGuard->clear();
     }
 
+    // Synchronize parse status across all ranks. This serves two purposes:
+    // 1. Propagate rank 0 failure to all ranks (parsing only happens on rank 0)
+    // 2. Ensure all ranks throw together, enabling cooperative shutdown
+    //    via Main::~Main() destructor calling MPI_Finalize()
     parseSuccess = comm.min(parseSuccess);
 
     if (! parseSuccess) {
@@ -787,11 +791,11 @@ void Opm::readDeck(Opm::Parallel::Communication    comm,
             OpmLog::error(fmt::format("Unrecoverable errors while loading input:\n{}", failureMessage));
         }
 
-#if HAVE_MPI
-        MPI_Finalize();
-#endif
-
-        std::exit(EXIT_FAILURE);
+        // Throw instead of std::exit() so that callers can handle the
+        // error. In production, Main::initialize_() catches this and
+        // returns false for cooperative shutdown. In unit tests,
+        // Boost.Test catches it and reports a proper test failure.
+        throw std::runtime_error(failureMessage);
     }
 }