diff --git a/src/index/IndexImpl.Text.cpp b/src/index/IndexImpl.Text.cpp
index b793189d6a..08afa9a112 100644
--- a/src/index/IndexImpl.Text.cpp
+++ b/src/index/IndexImpl.Text.cpp
@@ -23,7 +23,7 @@
 
 // _____________________________________________________________________________
 cppcoro::generator<WordsFileLine> IndexImpl::wordsInTextRecords(
-    const std::string& contextFile, bool addWordsFromLiterals) {
+    const std::string& contextFile, bool addWordsFromLiterals) const {
   auto localeManager = textVocab_.getLocaleManager();
   // ROUND 1: If context file aka wordsfile is not empty, read words from there.
   // Remember the last context id for the (optional) second round.
diff --git a/src/index/IndexImpl.h b/src/index/IndexImpl.h
index 5ce5eeaea3..1b491b04ab 100644
--- a/src/index/IndexImpl.h
+++ b/src/index/IndexImpl.h
@@ -522,7 +522,7 @@ class IndexImpl {
   // testing phase, once it works, it should be easy to include the IRIs and
   // literals from the external vocabulary as well).
   cppcoro::generator<WordsFileLine> wordsInTextRecords(
-      const std::string& contextFile, bool addWordsFromLiterals);
+      const std::string& contextFile, bool addWordsFromLiterals) const;
 
   size_t processWordsForVocabulary(const string& contextFile,
                                    bool addWordsFromLiterals);
diff --git a/src/parser/WordsAndDocsFileParser.cpp b/src/parser/WordsAndDocsFileParser.cpp
index 35bd955700..d5756e01d4 100644
--- a/src/parser/WordsAndDocsFileParser.cpp
+++ b/src/parser/WordsAndDocsFileParser.cpp
@@ -11,30 +11,32 @@
 #include "util/StringUtils.h"
 
 // _____________________________________________________________________________
-WordsAndDocsFileParser::WordsAndDocsFileParser(const string& wordsOrDocsFile,
-                                               LocaleManager localeManager)
-    : in_(wordsOrDocsFile), localeManager_(std::move(localeManager)) {}
+WordsAndDocsFileParser::WordsAndDocsFileParser(
+    const string& wordsOrDocsFile, const LocaleManager& localeManager)
+    : in_(wordsOrDocsFile), localeManager_(localeManager) {}
 
 // _____________________________________________________________________________
 ad_utility::InputRangeFromGet<WordsFileLine>::Storage WordsFileParser::get() {
   WordsFileLine line;
   string l;
-  if (!std::getline(in_, l)) {
+  if (!std::getline(getInputStream(), l)) {
     return std::nullopt;
   };
-  size_t i = l.find('\t');
+  std::string_view lineView(l);
+  size_t i = lineView.find('\t');
   assert(i != string::npos);
   size_t j = i + 2;
-  assert(j + 3 < l.size());
-  size_t k = l.find('\t', j + 2);
+  assert(j + 3 < lineView.size());
+  size_t k = lineView.find('\t', j + 2);
   assert(k != string::npos);
-  line.isEntity_ = (l[i + 1] == '1');
+  line.isEntity_ = (lineView[i + 1] == '1');
   line.word_ =
-      (line.isEntity_ ? l.substr(0, i)
-                      : localeManager_.getLowercaseUtf8(l.substr(0, i)));
+      (line.isEntity_
+           ? lineView.substr(0, i)
+           : getLocaleManager().getLowercaseUtf8(lineView.substr(0, i)));
   line.contextId_ =
-      TextRecordIndex::make(atol(l.substr(j + 1, k - j - 1).c_str()));
-  line.score_ = static_cast<Score>(atol(l.substr(k + 1).c_str()));
+      TextRecordIndex::make(atol(lineView.substr(j + 1, k - j - 1).data()));
+  line.score_ = static_cast<Score>(atol(lineView.substr(k + 1).data()));
 #ifndef NDEBUG
   if (lastCId_ > line.contextId_) {
     AD_THROW("ContextFile has to be sorted by context Id.");
@@ -48,7 +50,7 @@ ad_utility::InputRangeFromGet<WordsFileLine>::Storage WordsFileParser::get() {
 ad_utility::InputRangeFromGet<DocsFileLine>::Storage DocsFileParser::get() {
   DocsFileLine line;
   string l;
-  if (!std::getline(in_, l)) {
+  if (!std::getline(getInputStream(), l)) {
     return std::nullopt;
   };
   size_t i = l.find('\t');
diff --git a/src/parser/WordsAndDocsFileParser.h b/src/parser/WordsAndDocsFileParser.h
index 8365783a19..ebacfc2ebe 100644
--- a/src/parser/WordsAndDocsFileParser.h
+++ b/src/parser/WordsAndDocsFileParser.h
@@ -101,7 +101,7 @@ struct DocsFileLine {
 // The `Find` function returns the next delimiter in `text` after the given
 // `pos` or an empty substring if there is no next delimiter.
 struct LiteralsTokenizationDelimiter {
-  absl::string_view Find(absl::string_view text, size_t pos) {
+  absl::string_view Find(absl::string_view text, size_t pos) const {
     auto isWordChar = [](char c) -> bool { return std::isalnum(c); };
     auto found = std::find_if_not(text.begin() + pos, text.end(), isWordChar);
     if (found == text.end()) return text.substr(text.size());
@@ -138,12 +138,16 @@ inline auto tokenizeAndNormalizeText(std::string_view text,
 class WordsAndDocsFileParser {
  public:
   explicit WordsAndDocsFileParser(const string& wordsOrDocsFile,
-                                  LocaleManager localeManager);
+                                  const LocaleManager& localeManager);
   explicit WordsAndDocsFileParser(const WordsAndDocsFileParser& other) = delete;
   WordsAndDocsFileParser& operator=(const WordsAndDocsFileParser& other) =
       delete;
 
  protected:
+  std::ifstream& getInputStream() { return in_; }
+  const LocaleManager& getLocaleManager() { return localeManager_; }
+
+ private:
   std::ifstream in_;
   LocaleManager localeManager_;
 };
@@ -165,8 +169,8 @@ class WordsFileParser : public WordsAndDocsFileParser,
   using WordsAndDocsFileParser::WordsAndDocsFileParser;
   Storage get() override;
 
- private:
 #ifndef NDEBUG
+ private:
   // Only used for sanity checks in debug builds
   TextRecordIndex lastCId_ = TextRecordIndex::make(0);
 #endif