diff --git a/src/plugins/cpptools/clangdiagnosticconfigswidget.cpp b/src/plugins/cpptools/clangdiagnosticconfigswidget.cpp
index 6b8a04ac337..288b5e3a8d7 100644
--- a/src/plugins/cpptools/clangdiagnosticconfigswidget.cpp
+++ b/src/plugins/cpptools/clangdiagnosticconfigswidget.cpp
@@ -28,6 +28,7 @@
 
 #include <utils/algorithm.h>
 #include <utils/qtcassert.h>
+#include <utils/utilsicons.h>
 
 #include <QDebug>
 #include <QInputDialog>
@@ -107,15 +108,61 @@ void ClangDiagnosticConfigsWidget::onRemoveButtonClicked()
     syncConfigChooserToModel();
 }
 
+static bool isAcceptedWarningOption(const QString &option)
+{
+    return option == "-w"
+        || option == "-pedantic"
+        || option == "-pedantic-errors";
+}
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
+// https://clang.llvm.org/docs/DiagnosticsReference.html
+static bool isValidOption(const QString &option)
+{
+    if (option == "-Werror")
+        return false; // Avoid errors due to unknown or misspelled warnings.
+    return option.startsWith("-W") || isAcceptedWarningOption(option);
+}
+
+static QString validateDiagnosticOptions(const QStringList &options)
+{
+    // This is handy for testing, allow disabling validation.
+    if (qEnvironmentVariableIntValue("QTC_CLANG_NO_DIAGNOSTIC_CHECK"))
+        return QString();
+
+    for (const QString &option : options) {
+        if (!isValidOption(option))
+            return ClangDiagnosticConfigsWidget::tr("Option \"%1\" is invalid.").arg(option);
+    }
+
+    return QString();
+}
+
+static QStringList normalizeDiagnosticInputOptions(const QString &options)
+{
+    return options.simplified().split(QLatin1Char(' '), QString::SkipEmptyParts);
+}
+
 void ClangDiagnosticConfigsWidget::onDiagnosticOptionsEdited()
 {
-    const QString diagnosticOptions
-            = m_ui->diagnosticOptionsTextEdit->document()->toPlainText().trimmed();
-    const QStringList updatedCommandLine
-            = diagnosticOptions.trimmed().split(QLatin1Char(' '), QString::SkipEmptyParts);
+    // Clean up input
+    const QString diagnosticOptions = m_ui->diagnosticOptionsTextEdit->document()->toPlainText();
+    const QStringList normalizedOptions = normalizeDiagnosticInputOptions(diagnosticOptions);
 
+    // Validate
+    const QString errorMessage = validateDiagnosticOptions(normalizedOptions);
+    updateValidityWidgets(errorMessage);
+    if (!errorMessage.isEmpty()) {
+        // Remember the entered options in case the user will switch back.
+        m_notAcceptedOptions.insert(currentConfigId(), diagnosticOptions);
+        return;
+    }
+    m_notAcceptedOptions.remove(currentConfigId());
+
+    // Commit valid changes
     ClangDiagnosticConfig updatedConfig = currentConfig();
-    updatedConfig.setCommandLineWarnings(updatedCommandLine);
+    updatedConfig.setCommandLineWarnings(normalizedOptions);
 
     m_diagnosticConfigsModel.appendOrUpdate(updatedConfig);
     emit customConfigsChanged(customConfigs());
@@ -167,8 +214,10 @@ void ClangDiagnosticConfigsWidget::syncOtherWidgetsToComboBox()
     m_ui->removeButton->setEnabled(!config.isReadOnly());
 
     // Update child widgets
-    const QString commandLineWarnings = config.commandLineWarnings().join(QLatin1Char(' '));
-    setDiagnosticOptions(commandLineWarnings);
+    const QString options = m_notAcceptedOptions.contains(config.id())
+            ? m_notAcceptedOptions.value(config.id())
+            : config.commandLineWarnings().join(QLatin1Char(' '));
+    setDiagnosticOptions(options);
     m_ui->diagnosticOptionsTextEdit->setReadOnly(config.isReadOnly());
 }
 
@@ -186,11 +235,35 @@ void ClangDiagnosticConfigsWidget::setDiagnosticOptions(const QString &options)
 {
     if (options != m_ui->diagnosticOptionsTextEdit->document()->toPlainText()) {
         disconnectDiagnosticOptionsChanged();
+
         m_ui->diagnosticOptionsTextEdit->document()->setPlainText(options);
+        const QString errorMessage
+                = validateDiagnosticOptions(normalizeDiagnosticInputOptions(options));
+        updateValidityWidgets(errorMessage);
+
         connectDiagnosticOptionsChanged();
     }
 }
 
+void ClangDiagnosticConfigsWidget::updateValidityWidgets(const QString &errorMessage)
+{
+    QString validationResult;
+    const Utils::Icon *icon = nullptr;
+    QString styleSheet;
+    if (errorMessage.isEmpty()) {
+        icon = &Utils::Icons::INFO;
+        validationResult = tr("Configuration passes sanity checks.");
+    } else {
+        icon = &Utils::Icons::CRITICAL;
+        validationResult = tr("%1").arg(errorMessage);
+        styleSheet = "color: red;";
+    }
+
+    m_ui->validationResultIcon->setPixmap(icon->pixmap());
+    m_ui->validationResultLabel->setText(validationResult);
+    m_ui->validationResultLabel->setStyleSheet(styleSheet);
+}
+
 void ClangDiagnosticConfigsWidget::connectConfigChooserCurrentIndex()
 {
     connect(m_ui->configChooserComboBox,
diff --git a/src/plugins/cpptools/clangdiagnosticconfigswidget.h b/src/plugins/cpptools/clangdiagnosticconfigswidget.h
index e22de1b97d0..ff11815a229 100644
--- a/src/plugins/cpptools/clangdiagnosticconfigswidget.h
+++ b/src/plugins/cpptools/clangdiagnosticconfigswidget.h
@@ -30,6 +30,7 @@
 #include "clangdiagnosticconfig.h"
 #include "clangdiagnosticconfigsmodel.h"
 
+#include <QHash>
 #include <QWidget>
 
 namespace CppTools {
@@ -72,6 +73,7 @@ private:
     const ClangDiagnosticConfig &currentConfig() const;
 
     void setDiagnosticOptions(const QString &options);
+    void updateValidityWidgets(const QString &errorMessage);
 
     void connectConfigChooserCurrentIndex();
     void disconnectConfigChooserCurrentIndex();
@@ -81,6 +83,7 @@ private:
 private:
     Ui::ClangDiagnosticConfigsWidget *m_ui;
     ClangDiagnosticConfigsModel m_diagnosticConfigsModel;
+    QHash<Core::Id, QString> m_notAcceptedOptions;
 };
 
 } // CppTools namespace
diff --git a/src/plugins/cpptools/clangdiagnosticconfigswidget.ui b/src/plugins/cpptools/clangdiagnosticconfigswidget.ui
index 25d0c0b598d..e07ffb7b063 100644
--- a/src/plugins/cpptools/clangdiagnosticconfigswidget.ui
+++ b/src/plugins/cpptools/clangdiagnosticconfigswidget.ui
@@ -6,7 +6,7 @@
    <rect>
     <x>0</x>
     <y>0</y>
-    <width>597</width>
+    <width>665</width>
     <height>300</height>
    </rect>
   </property>
@@ -14,18 +14,6 @@
    <string>Form</string>
   </property>
   <layout class="QVBoxLayout" name="verticalLayout">
-   <property name="leftMargin">
-    <number>0</number>
-   </property>
-   <property name="topMargin">
-    <number>0</number>
-   </property>
-   <property name="rightMargin">
-    <number>0</number>
-   </property>
-   <property name="bottomMargin">
-    <number>0</number>
-   </property>
    <item>
     <layout class="QHBoxLayout" name="horizontalLayout">
      <item>
@@ -61,6 +49,37 @@
      </item>
     </layout>
    </item>
+   <item>
+    <layout class="QHBoxLayout" name="horizontalLayout_2">
+     <item>
+      <widget class="QLabel" name="validationResultIcon">
+       <property name="text">
+        <string>ValidationIcon</string>
+       </property>
+      </widget>
+     </item>
+     <item>
+      <widget class="QLabel" name="validationResultLabel">
+       <property name="text">
+        <string>ValidationText</string>
+       </property>
+      </widget>
+     </item>
+     <item>
+      <spacer name="horizontalSpacer">
+       <property name="orientation">
+        <enum>Qt::Horizontal</enum>
+       </property>
+       <property name="sizeHint" stdset="0">
+        <size>
+         <width>40</width>
+         <height>20</height>
+        </size>
+       </property>
+      </spacer>
+     </item>
+    </layout>
+   </item>
    <item>
     <widget class="QPlainTextEdit" name="diagnosticOptionsTextEdit"/>
    </item>