diff --git a/ProcessLib/CompareJacobiansJacobianAssembler.cpp b/ProcessLib/CompareJacobiansJacobianAssembler.cpp
index 776c55a9729b7e1126ff2f6ffa376b5248ad00c4..84d03f82396c5919e7072255a688b2c9e0386536 100644
--- a/ProcessLib/CompareJacobiansJacobianAssembler.cpp
+++ b/ProcessLib/CompareJacobiansJacobianAssembler.cpp
@@ -380,11 +380,13 @@ void CompareJacobiansJacobianAssembler::assembleWithJacobian(
 
     if (fatal_error)
     {
+        _log_file << std::flush;
         OGS_FATAL("%s", msg_fatal.c_str());
     }
 
     if (tol_exceeded && _fail_on_error)
     {
+        _log_file << std::flush;
         OGS_FATAL(
             "OGS failed, because the two Jacobian implementations returned "
             "different results.");