diff --git a/src/plugins/cppeditor/cppeditor.cpp b/src/plugins/cppeditor/cppeditor.cpp
index e490c4fbe33..ce276c363b9 100644
--- a/src/plugins/cppeditor/cppeditor.cpp
+++ b/src/plugins/cppeditor/cppeditor.cpp
@@ -715,6 +715,7 @@ void CPPEditorWidget::setMimeType(const QString &mt)
 
     QSharedPointer<SnapshotUpdater> updater
             = m_modelManager->cppEditorSupport(editor())->snapshotUpdater();
+    updater->setProjectPart(m_modelManager->projectPartForProjectFile(projectFile));
     updater->setEditorDefines(additionalDirectives);
 
     m_preprocessorButton->setProperty("highlightWidget", !additionalDirectives.trimmed().isEmpty());
@@ -1994,6 +1995,7 @@ void CPPEditorWidget::showPreProcessorWidget()
         QSharedPointer<SnapshotUpdater> updater
                 = m_modelManager->cppEditorSupport(editor())->snapshotUpdater();
         const QString &additionals = preProcessorDialog.additionalPreProcessorDirectives();
+        updater->setProjectPart(preProcessorDialog.projectPart());
         updater->setEditorDefines(additionals.toUtf8());
         updater->update(m_modelManager->workingCopy());
 
diff --git a/src/plugins/cppeditor/cpppreprocessordialog.cpp b/src/plugins/cppeditor/cpppreprocessordialog.cpp
index e9649625559..983bbe9aca3 100644
--- a/src/plugins/cppeditor/cpppreprocessordialog.cpp
+++ b/src/plugins/cppeditor/cpppreprocessordialog.cpp
@@ -112,6 +112,11 @@ int CppPreProcessorDialog::exec()
     return Accepted;
 }
 
+CppTools::ProjectPart::Ptr CppPreProcessorDialog::projectPart() const
+{
+    return m_partAdditions[m_ui->projectComboBox->currentIndex()].projectPart;
+}
+
 QString CppPreProcessorDialog::additionalPreProcessorDirectives() const
 {
     return m_ui->editWidget->toPlainText();
diff --git a/src/plugins/cppeditor/cpppreprocessordialog.h b/src/plugins/cppeditor/cpppreprocessordialog.h
index c56e397fe11..c71e387e874 100644
--- a/src/plugins/cppeditor/cpppreprocessordialog.h
+++ b/src/plugins/cppeditor/cpppreprocessordialog.h
@@ -50,6 +50,8 @@ public:
     ~CppPreProcessorDialog();
 
     int exec();
+
+    CppTools::ProjectPart::Ptr projectPart() const;
     QString additionalPreProcessorDirectives() const;
 
 private slots:
diff --git a/src/plugins/cpptools/cppmodelmanager.cpp b/src/plugins/cpptools/cppmodelmanager.cpp
index cbf11126bc8..bbe1a481aae 100644
--- a/src/plugins/cpptools/cppmodelmanager.cpp
+++ b/src/plugins/cpptools/cppmodelmanager.cpp
@@ -689,12 +689,14 @@ private:
 /// Make sure that m_projectMutex is locked when calling this.
 void CppModelManager::recalculateFileToProjectParts()
 {
+    m_projectFileToProjectPart.clear();
     m_fileToProjectParts.clear();
     foreach (const ProjectInfo &projectInfo, m_projectToProjectsInfo) {
         foreach (const ProjectPart::Ptr &projectPart, projectInfo.projectParts()) {
-            foreach (const ProjectFile &cxxFile, projectPart->files) {
+            m_projectFileToProjectPart[projectPart->projectFile] = projectPart;
+            foreach (const ProjectFile &cxxFile, projectPart->files)
                 m_fileToProjectParts[cxxFile.path].append(projectPart);
-            }
+
         }
     }
 }
@@ -774,6 +776,11 @@ QFuture<void> CppModelManager::updateProjectInfo(const ProjectInfo &newProjectIn
     return updateSourceFiles(filesToReindex, ForcedProgressNotification);
 }
 
+ProjectPart::Ptr CppModelManager::projectPartForProjectFile(const QString &projectFile) const
+{
+    return m_projectFileToProjectPart.value(projectFile);
+}
+
 QList<ProjectPart::Ptr> CppModelManager::projectPart(const QString &fileName) const
 {
     return m_fileToProjectParts.value(fileName);
diff --git a/src/plugins/cpptools/cppmodelmanager.h b/src/plugins/cpptools/cppmodelmanager.h
index 0bc4ee750d4..3bddb955ad9 100644
--- a/src/plugins/cpptools/cppmodelmanager.h
+++ b/src/plugins/cpptools/cppmodelmanager.h
@@ -75,6 +75,8 @@ public:
     virtual ProjectInfo projectInfo(ProjectExplorer::Project *project) const;
     virtual QFuture<void> updateProjectInfo(const ProjectInfo &newProjectInfo);
 
+    /// \return The project part with the given project file
+    virtual ProjectPart::Ptr projectPartForProjectFile(const QString &projectFile) const;
     /// \return All project parts that mention the given file name as one of the sources/headers.
     virtual QList<ProjectPart::Ptr> projectPart(const QString &fileName) const;
     /// This is a fall-back function: find all files that includes the file directly or indirectly,
@@ -199,6 +201,7 @@ private:
     mutable QMutex m_projectMutex;
     QMap<ProjectExplorer::Project *, ProjectInfo> m_projectToProjectsInfo;
     QMap<QString, QList<CppTools::ProjectPart::Ptr> > m_fileToProjectParts;
+    QMap<QString, CppTools::ProjectPart::Ptr> m_projectFileToProjectPart;
     // The members below are cached/(re)calculated from the projects and/or their project parts
     bool m_dirty;
     QStringList m_projectFiles;
diff --git a/src/plugins/cpptools/cppmodelmanagerinterface.h b/src/plugins/cpptools/cppmodelmanagerinterface.h
index 49a9eea066f..2cc0cbae647 100644
--- a/src/plugins/cpptools/cppmodelmanagerinterface.h
+++ b/src/plugins/cpptools/cppmodelmanagerinterface.h
@@ -233,6 +233,7 @@ public:
     virtual QList<ProjectInfo> projectInfos() const = 0;
     virtual ProjectInfo projectInfo(ProjectExplorer::Project *project) const = 0;
     virtual QFuture<void> updateProjectInfo(const ProjectInfo &pinfo) = 0;
+    virtual ProjectPart::Ptr projectPartForProjectFile(const QString &projectFile) const = 0;
     virtual QList<ProjectPart::Ptr> projectPart(const QString &fileName) const = 0;
     virtual QList<ProjectPart::Ptr> projectPartFromDependencies(const QString &fileName) const = 0;
     virtual ProjectPart::Ptr fallbackProjectPart() const = 0;