diff --git a/src/Mod/Fem/Gui/DlgSettingsFemElmerImp.cpp b/src/Mod/Fem/Gui/DlgSettingsFemElmerImp.cpp
index cf9808a555..7d74ce4e22 100644
--- a/src/Mod/Fem/Gui/DlgSettingsFemElmerImp.cpp
+++ b/src/Mod/Fem/Gui/DlgSettingsFemElmerImp.cpp
@@ -116,9 +116,12 @@ void DlgSettingsFemElmerImp::onfileNameChangedMT(QString FileName)
         return;
 
     auto strName = FileName.toStdString();
+
+    // strName can be empty if there was once a valid Elmer installation but Elmer was meanwhile
+    // removed. That strName is shorter than 9 can only happen if the user.cfg file is corrupted.
 #if defined(FC_OS_WIN32)
     // name ends with "_mpi.exe"
-    if (strName.empty() || strName.substr(strName.length() - 8) != "_mpi.exe") {
+    if (strName.length() < 9 || strName.substr(strName.length() - 8) != "_mpi.exe") {
         QMessageBox::warning(this, tr("FEM Elmer: Not suitable for multithreading"),
             tr("Wrong Elmer setting: You use more than one CPU core.\n"
                 "Therefore an executable with the suffix '_mpi.exe' is required."));
@@ -128,7 +131,7 @@ void DlgSettingsFemElmerImp::onfileNameChangedMT(QString FileName)
     }
 #elif defined(FC_OS_LINUX) || defined(FC_OS_CYGWIN) || defined(FC_OS_MACOSX) || defined(FC_OS_BSD)
     // name ends with "_mpi"
-    if (strName.empty() || strName.substr(strName.length() - 4) != "_mpi") {
+    if (strName.length() < 9 || strName.substr(strName.length() - 4) != "_mpi") {
         QMessageBox::warning(this, tr("FEM Elmer: Not suitable for multithreading"),
             tr("Wrong Elmer setting: You use more than one CPU core.\n"
                 "Therefore an executable with the suffix '_mpi' is required."));