diff --git a/src/tools/clangpchmanagerbackend/source/pchcreator.cpp b/src/tools/clangpchmanagerbackend/source/pchcreator.cpp
index 46562c39a9b..3aa8b3c5169 100644
--- a/src/tools/clangpchmanagerbackend/source/pchcreator.cpp
+++ b/src/tools/clangpchmanagerbackend/source/pchcreator.cpp
@@ -112,7 +112,7 @@ Utils::SmallStringVector PchCreator::generateClangCompilerArguments(const PchTas
     return builder.commandLine;
 }
 
-FilePathIds PchCreator::existingSources(FilePathIds sources) const
+FilePathIds PchCreator::existingSources(const FilePathIds &sources) const
 {
     FilePathIds existingSources;
     existingSources.reserve(sources.size());
diff --git a/src/tools/clangpchmanagerbackend/source/pchcreator.h b/src/tools/clangpchmanagerbackend/source/pchcreator.h
index c30e0110111..bc217d59e7b 100644
--- a/src/tools/clangpchmanagerbackend/source/pchcreator.h
+++ b/src/tools/clangpchmanagerbackend/source/pchcreator.h
@@ -82,7 +82,7 @@ public:
 
     const ClangTool &clangTool() const { return m_clangTool; }
 
-    FilePathIds existingSources(FilePathIds sources) const;
+    FilePathIds existingSources(const FilePathIds &sources) const;
 
     const FilePathIds &watchedSystemIncludes() const { return m_watchedSystemIncludes; }
     const FilePathIds &watchedProjectIncludes() const { return m_watchedProjectIncludes; }