diff --git a/src/tools/clangbackend/ipcsource/clangipcserver.cpp b/src/tools/clangbackend/ipcsource/clangipcserver.cpp
index 7165ed24a51..ac04f932030 100644
--- a/src/tools/clangbackend/ipcsource/clangipcserver.cpp
+++ b/src/tools/clangbackend/ipcsource/clangipcserver.cpp
@@ -193,6 +193,8 @@ void ClangIpcServer::registerProjectPartsForEditor(const RegisterProjectPartsFor
 
     try {
         projects.createOrUpdate(message.projectContainers());
+        translationUnits.setTranslationUnitsDirtyIfProjectPartChanged();
+        sendDocumentAnnotationsTimer.start(0);
     } catch (const std::exception &exception) {
         qWarning() << "Error in ClangIpcServer::registerProjectPartsForEditor:" << exception.what();
     }
diff --git a/src/tools/clangbackend/ipcsource/clangtranslationunit.cpp b/src/tools/clangbackend/ipcsource/clangtranslationunit.cpp
index 5df086781ff..4954cd79048 100644
--- a/src/tools/clangbackend/ipcsource/clangtranslationunit.cpp
+++ b/src/tools/clangbackend/ipcsource/clangtranslationunit.cpp
@@ -276,13 +276,16 @@ const QSet<Utf8String> &TranslationUnit::dependedFilePaths() const
     return d->dependedFilePaths;
 }
 
+void TranslationUnit::setDirtyIfProjectPartIsOutdated()
+{
+    if (projectPartIsOutdated())
+        setDirty();
+}
+
 void TranslationUnit::setDirtyIfDependencyIsMet(const Utf8String &filePath)
 {
-    if (d->dependedFilePaths.contains(filePath) && isMainFileAndExistsOrIsOtherFile(filePath)) {
-        d->needsToBeReparsed = true;
-        d->hasNewDiagnostics = true;
-        d->hasNewHighlightingInformations = true;
-    }
+    if (d->dependedFilePaths.contains(filePath) && isMainFileAndExistsOrIsOtherFile(filePath))
+        setDirty();
 }
 
 SourceLocation TranslationUnit::sourceLocationAt(uint line, uint column) const
@@ -369,6 +372,13 @@ bool TranslationUnit::projectPartIsOutdated() const
     return d->projectPart.lastChangeTimePoint() >= d->lastProjectPartChangeTimePoint;
 }
 
+void TranslationUnit::setDirty()
+{
+    d->needsToBeReparsed = true;
+    d->hasNewDiagnostics = true;
+    d->hasNewHighlightingInformations = true;
+}
+
 bool TranslationUnit::isMainFileAndExistsOrIsOtherFile(const Utf8String &filePath) const
 {
     if (filePath == d->filePath)
diff --git a/src/tools/clangbackend/ipcsource/clangtranslationunit.h b/src/tools/clangbackend/ipcsource/clangtranslationunit.h
index 61d58c804cd..016067dc369 100644
--- a/src/tools/clangbackend/ipcsource/clangtranslationunit.h
+++ b/src/tools/clangbackend/ipcsource/clangtranslationunit.h
@@ -120,6 +120,7 @@ public:
 
     const QSet<Utf8String> &dependedFilePaths() const;
 
+    void setDirtyIfProjectPartIsOutdated();
     void setDirtyIfDependencyIsMet(const Utf8String &filePath);
 
     CommandLineArguments commandLineArguments() const;
@@ -139,6 +140,7 @@ public:
     SkippedSourceRanges skippedSourceRanges() const;
 
 private:
+    void setDirty();
     void checkIfNull() const;
     void checkIfFileExists() const;
     void updateLastProjectPartChangeTimePoint() const;
diff --git a/src/tools/clangbackend/ipcsource/projectpart.h b/src/tools/clangbackend/ipcsource/projectpart.h
index 7272fd0a89e..6904ba35fdf 100644
--- a/src/tools/clangbackend/ipcsource/projectpart.h
+++ b/src/tools/clangbackend/ipcsource/projectpart.h
@@ -31,11 +31,12 @@
 #ifndef CLANGBACKEND_PROJECT_H
 #define CLANGBACKEND_PROJECT_H
 
+#include <utf8string.h>
+
 #include <chrono>
 #include <memory>
 #include <vector>
 
-class Utf8String;
 class Utf8StringVector;
 
 namespace ClangBackEnd {
@@ -48,7 +49,7 @@ using time_point = std::chrono::steady_clock::time_point;
 class ProjectPart
 {
 public:
-    ProjectPart(const Utf8String &projectPartId);
+    ProjectPart(const Utf8String &projectPartId = Utf8String());
     ProjectPart(const Utf8String &projectPartId,
                 std::initializer_list<Utf8String> arguments);
     ProjectPart(const ProjectPartContainer &projectContainer);
diff --git a/src/tools/clangbackend/ipcsource/translationunits.cpp b/src/tools/clangbackend/ipcsource/translationunits.cpp
index 885eabaefae..ad84e0a3797 100644
--- a/src/tools/clangbackend/ipcsource/translationunits.cpp
+++ b/src/tools/clangbackend/ipcsource/translationunits.cpp
@@ -170,6 +170,12 @@ void TranslationUnits::updateTranslationUnitsWithChangedDependencies(const QVect
         updateTranslationUnitsWithChangedDependency(fileContainer.filePath());
 }
 
+void TranslationUnits::setTranslationUnitsDirtyIfProjectPartChanged()
+{
+    for (auto &translationUnit : translationUnits_)
+        translationUnit.setDirtyIfProjectPartIsOutdated();
+}
+
 DocumentAnnotationsSendState TranslationUnits::sendDocumentAnnotations()
 {
     auto documentAnnotationsSendState = sendDocumentAnnotationsForCurrentEditor();
diff --git a/src/tools/clangbackend/ipcsource/translationunits.h b/src/tools/clangbackend/ipcsource/translationunits.h
index 49ed36e7e29..28a1cb7b766 100644
--- a/src/tools/clangbackend/ipcsource/translationunits.h
+++ b/src/tools/clangbackend/ipcsource/translationunits.h
@@ -83,6 +83,7 @@ public:
 
     void updateTranslationUnitsWithChangedDependency(const Utf8String &filePath);
     void updateTranslationUnitsWithChangedDependencies(const QVector<FileContainer> &fileContainers);
+    void setTranslationUnitsDirtyIfProjectPartChanged();
 
     DocumentAnnotationsSendState sendDocumentAnnotationsForCurrentEditor();
     DocumentAnnotationsSendState sendDocumentAnnotationsForVisibleEditors();
diff --git a/tests/unit/unittest/translationunitstest.cpp b/tests/unit/unittest/translationunitstest.cpp
index 32414739674..3e4b9d9cf94 100644
--- a/tests/unit/unittest/translationunitstest.cpp
+++ b/tests/unit/unittest/translationunitstest.cpp
@@ -57,6 +57,7 @@
 using ClangBackEnd::TranslationUnit;
 using ClangBackEnd::UnsavedFiles;
 using ClangBackEnd::ProjectPart;
+using ClangBackEnd::ProjectPartContainer;
 using ClangBackEnd::DiagnosticsChangedMessage;
 using ClangBackEnd::HighlightingChangedMessage;
 using ClangBackEnd::DocumentAnnotationsSendState;
@@ -483,9 +484,24 @@ TEST_F(TranslationUnits, SendDocumentAnnotationsOnlyOnceForVisibleEditor)
     sendAllDocumentAnnotationsForVisibleEditors();
 }
 
+TEST_F(TranslationUnits, SendDocumentAnnotationsAfterProjectPartChange)
+{
+    translationUnits.create({fileContainer, headerContainer});
+    auto fileTranslationUnit = translationUnits.translationUnit(fileContainer);
+    fileTranslationUnit.setIsVisibleInEditor(true);
+    fileTranslationUnit.diagnostics(); // Reset
+    fileTranslationUnit.highlightingInformations(); // Reset
+    projects.createOrUpdate({ProjectPartContainer(projectPartId, {Utf8StringLiteral("-DNEW")})});
+    translationUnits.setTranslationUnitsDirtyIfProjectPartChanged();
+
+    EXPECT_CALL(mockSendDocumentAnnotationsCallback, sendDocumentAnnotations()).Times(1);
+
+    sendAllDocumentAnnotationsForVisibleEditors();
+}
+
 void TranslationUnits::SetUp()
 {
-    projects.createOrUpdate({ClangBackEnd::ProjectPartContainer(projectPartId)});
+    projects.createOrUpdate({ProjectPartContainer(projectPartId)});
 
     auto callback = [&] (const DiagnosticsChangedMessage &, const HighlightingChangedMessage &) {
         mockSendDocumentAnnotationsCallback.sendDocumentAnnotations();
diff --git a/tests/unit/unittest/translationunittest.cpp b/tests/unit/unittest/translationunittest.cpp
index 24bdcdac101..579f71bd61f 100644
--- a/tests/unit/unittest/translationunittest.cpp
+++ b/tests/unit/unittest/translationunittest.cpp
@@ -33,6 +33,7 @@
 #include <highlightinginformations.h>
 #include <filecontainer.h>
 #include <projectpart.h>
+#include <projectpartcontainer.h>
 #include <projects.h>
 #include <translationunitdoesnotexistexception.h>
 #include <translationunitfilenotexitexception.h>
@@ -55,10 +56,11 @@
 #include <chrono>
 #include <thread>
 
-
+using ClangBackEnd::FileContainer;
 using ClangBackEnd::TranslationUnit;
 using ClangBackEnd::UnsavedFiles;
 using ClangBackEnd::ProjectPart;
+using ClangBackEnd::ProjectPartContainer;
 using ClangBackEnd::TranslationUnits;
 
 using testing::IsNull;
@@ -74,19 +76,18 @@ namespace {
 class TranslationUnit : public ::testing::Test
 {
 protected:
+    void SetUp() override;
     ::TranslationUnit createTemporaryTranslationUnit();
     QByteArray readContentFromTranslationUnitFile() const;
 
 protected:
     ClangBackEnd::ProjectParts projects;
-    ProjectPart projectPart{Utf8StringLiteral("/path/to/projectfile")};
+    Utf8String projectPartId{Utf8StringLiteral("/path/to/projectfile")};
+    ProjectPart projectPart;
     Utf8String translationUnitFilePath = Utf8StringLiteral(TESTDATA_DIR"/translationunits.cpp");
     ClangBackEnd::UnsavedFiles unsavedFiles;
     ClangBackEnd::TranslationUnits translationUnits{projects, unsavedFiles};
-    ::TranslationUnit translationUnit{translationUnitFilePath,
-                                      projectPart,
-                                      Utf8StringVector(),
-                                      translationUnits};
+    ::TranslationUnit translationUnit;
 };
 
 TEST_F(TranslationUnit, DefaultTranslationUnitIsInvalid)
@@ -338,6 +339,36 @@ TEST_F(TranslationUnit, HasNoNewHighlightingInformationsAfterGettingHighlighting
     ASSERT_FALSE(translationUnit.hasNewHighlightingInformations());
 }
 
+TEST_F(TranslationUnit, SetDirtyIfProjectPartIsOutdated)
+{
+    projects.createOrUpdate({ProjectPartContainer(projectPartId)});
+    translationUnit.cxTranslationUnit();
+    projects.createOrUpdate({ProjectPartContainer(projectPartId, {Utf8StringLiteral("-DNEW")})});
+
+    translationUnit.setDirtyIfProjectPartIsOutdated();
+
+    ASSERT_TRUE(translationUnit.isNeedingReparse());
+}
+
+TEST_F(TranslationUnit, SetNotDirtyIfProjectPartIsNotOutdated)
+{
+    translationUnit.cxTranslationUnit();
+
+    translationUnit.setDirtyIfProjectPartIsOutdated();
+
+    ASSERT_FALSE(translationUnit.isNeedingReparse());
+}
+
+void TranslationUnit::SetUp()
+{
+    projects.createOrUpdate({ProjectPartContainer(projectPartId)});
+    projectPart = *projects.findProjectPart(projectPartId);
+
+    const QVector<FileContainer> fileContainer{FileContainer(translationUnitFilePath, projectPartId)};
+    const auto createdTranslationUnits = translationUnits.create(fileContainer);
+    translationUnit = createdTranslationUnits.front();
+}
+
 ::TranslationUnit TranslationUnit::createTemporaryTranslationUnit()
 {
     QTemporaryFile temporaryFile;
@@ -348,7 +379,7 @@ TEST_F(TranslationUnit, HasNoNewHighlightingInformationsAfterGettingHighlighting
                                       Utf8StringVector(),
                                       translationUnits);
 
-return translationUnit;
+    return translationUnit;
 }
 
 QByteArray TranslationUnit::readContentFromTranslationUnitFile() const