diff --git a/src/libs/clangsupport/progresscounter.h b/src/libs/clangsupport/progresscounter.h
index fbdc9dda456..449754f9149 100644
--- a/src/libs/clangsupport/progresscounter.h
+++ b/src/libs/clangsupport/progresscounter.h
@@ -26,6 +26,7 @@
 #pragma once
 
 #include <functional>
+#include <mutex>
 
 namespace ClangBackEnd {
 
@@ -33,6 +34,7 @@ class ProgressCounter
 {
 public:
     using SetProgressCallback = std::function<void(int, int)>;
+    using Lock = std::lock_guard<std::mutex>;
 
     ProgressCounter(SetProgressCallback &&progressCallback)
         : m_progressCallback(std::move(progressCallback))
@@ -40,6 +42,8 @@ public:
 
     void addTotal(int total)
     {
+        Lock lock(m_mutex);
+
         if (total) {
             m_total += total;
 
@@ -49,6 +53,8 @@ public:
 
     void removeTotal(int total)
     {
+        Lock lock(m_mutex);
+
         if (total) {
             m_total -= total;
 
@@ -58,6 +64,8 @@ public:
 
     void addProgress(int progress)
     {
+        Lock lock(m_mutex);
+
         if (progress) {
             m_progress += progress;
 
@@ -65,6 +73,21 @@ public:
         }
     }
 
+    int total() const
+    {
+        Lock lock(m_mutex);
+
+        return m_total;
+    }
+
+    int progress() const
+    {
+        Lock lock(m_mutex);
+
+        return m_total;
+    }
+
+private:
     void sendProgress()
     {
         m_progressCallback(m_progress, m_total);
@@ -75,17 +98,8 @@ public:
         }
     }
 
-    int total() const
-    {
-        return m_total;
-    }
-
-    int progress() const
-    {
-        return m_total;
-    }
-
 private:
+    mutable std::mutex m_mutex;
     std::function<void(int, int)> m_progressCallback;
     int m_progress = 0;
     int m_total = 0;
diff --git a/src/tools/clangrefactoringbackend/clangrefactoringbackendmain.cpp b/src/tools/clangrefactoringbackend/clangrefactoringbackendmain.cpp
index 23a127c17f2..876c047fb85 100644
--- a/src/tools/clangrefactoringbackend/clangrefactoringbackendmain.cpp
+++ b/src/tools/clangrefactoringbackend/clangrefactoringbackendmain.cpp
@@ -51,6 +51,48 @@ using ClangBackEnd::RefactoringDatabaseInitializer;
 using ClangBackEnd::ConnectionServer;
 using ClangBackEnd::SymbolIndexing;
 
+#if QT_VERSION < QT_VERSION_CHECK(5, 10, 0)
+template<typename CallableType>
+class CallableEvent : public QEvent
+{
+public:
+    using Callable = std::decay_t<CallableType>;
+    CallableEvent(Callable &&callable)
+        : QEvent(QEvent::None)
+        , callable(std::move(callable))
+    {}
+    CallableEvent(const Callable &callable)
+        : QEvent(QEvent::None)
+        , callable(callable)
+    {}
+
+    ~CallableEvent() { callable(); }
+
+public:
+    Callable callable;
+};
+
+template<typename Callable>
+void executeInLoop(Callable &&callable, QObject *object = QCoreApplication::instance())
+{
+    if (QThread *thread = qobject_cast<QThread *>(object))
+        object = QAbstractEventDispatcher::instance(thread);
+
+    QCoreApplication::postEvent(object,
+                                new CallableEvent<Callable>(std::forward<Callable>(callable)),
+                                Qt::HighEventPriority);
+}
+#else
+template<typename Callable>
+void executeInLoop(Callable &&callable, QObject *object = QCoreApplication::instance())
+{
+    if (QThread *thread = qobject_cast<QThread *>(object))
+        object = QAbstractEventDispatcher::instance(thread);
+
+    QMetaObject::invokeMethod(object, std::forward<Callable>(callable));
+}
+#endif
+
 QStringList processArguments(QCoreApplication &application)
 {
     QCommandLineParser parser;
@@ -95,7 +137,14 @@ struct Data // because we have a cycle dependency
     FilePathCaching filePathCache{database};
     GeneratedFiles generatedFiles;
     RefactoringServer clangCodeModelServer{symbolIndexing, filePathCache, generatedFiles};
-    SymbolIndexing symbolIndexing{database, filePathCache, generatedFiles, [&] (int progress, int total) { clangCodeModelServer.setProgress(progress, total); }};
+    SymbolIndexing symbolIndexing{database,
+                                  filePathCache,
+                                  generatedFiles,
+                                  [&](int progress, int total) {
+                                      executeInLoop([&] {
+                                          clangCodeModelServer.setProgress(progress, total);
+                                      });
+                                  }};
 };
 
 #ifdef Q_OS_WIN
diff --git a/tests/unit/unittest/commandlinebuilder-test.cpp b/tests/unit/unittest/commandlinebuilder-test.cpp
index 3ec2b032246..3d684e10bca 100644
--- a/tests/unit/unittest/commandlinebuilder-test.cpp
+++ b/tests/unit/unittest/commandlinebuilder-test.cpp
@@ -417,7 +417,7 @@ TYPED_TEST(CommandLineBuilder, C18)
 
     Builder<TypeParam> builder{this->emptyProjectInfo, {}, InputFileType::Header, "/source/file.c"};
 
-    ASSERT_THAT(builder.commandLine, Contains("-std=c18"));
+    ASSERT_THAT(builder.commandLine, Contains("-std=c17"));
 }
 
 TYPED_TEST(CommandLineBuilder, GnuC89)
@@ -461,7 +461,7 @@ TYPED_TEST(CommandLineBuilder, GnuC18)
 
     Builder<TypeParam> builder{this->emptyProjectInfo, {}, InputFileType::Header, "/source/file.c"};
 
-    ASSERT_THAT(builder.commandLine, Contains("-std=gnu18"));
+    ASSERT_THAT(builder.commandLine, Contains("-std=gnu17"));
 }
 
 TYPED_TEST(CommandLineBuilder, IncludesOrder)