diff --git a/src/libexpr/include/nix/expr/eval.hh b/src/libexpr/include/nix/expr/eval.hh
index 75ed12664..f1cead47b 100644
--- a/src/libexpr/include/nix/expr/eval.hh
+++ b/src/libexpr/include/nix/expr/eval.hh
@@ -474,7 +474,8 @@ private:
 
     LookupPath lookupPath;
 
-    boost::unordered_flat_map<std::string, std::optional<SourcePath>> lookupPathResolved;
+    boost::unordered_flat_map<std::string, std::optional<SourcePath>, StringViewHash, std::equal_to<>>
+        lookupPathResolved;
 
     /**
      * Cache used by prim_match().
@@ -751,8 +752,8 @@ public:
     boost::unordered_flat_map<
         std::string,
         Value *,
-        std::hash<std::string>,
-        std::equal_to<std::string>,
+        StringViewHash,
+        std::equal_to<>,
         traceable_allocator<std::pair<const std::string, Value *>>>
         internalPrimOps;
 
@@ -1019,7 +1020,7 @@ private:
 
     bool countCalls;
 
-    typedef boost::unordered_flat_map<std::string, size_t> PrimOpCalls;
+    typedef boost::unordered_flat_map<std::string, size_t, StringViewHash, std::equal_to<>> PrimOpCalls;
     PrimOpCalls primOpCalls;
 
     typedef boost::unordered_flat_map<ExprLambda *, size_t> FunctionCalls;
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index dd33f5f84..fdbc670df 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -311,7 +311,12 @@ Roots LocalStore::findRoots(bool censor)
 /**
  * Key is a mere string because cannot has path with macOS's libc++
  */
-typedef boost::unordered_flat_map<std::string, boost::unordered_flat_set<std::string>> UncheckedRoots;
+typedef boost::unordered_flat_map<
+    std::string,
+    boost::unordered_flat_set<std::string, StringViewHash, std::equal_to<>>,
+    StringViewHash,
+    std::equal_to<>>
+    UncheckedRoots;
 
 static void readProcLink(const std::filesystem::path & file, UncheckedRoots & roots)
 {
@@ -325,7 +330,7 @@ static void readProcLink(const std::filesystem::path & file, UncheckedRoots & ro
         throw;
     }
     if (buf.is_absolute())
-        roots[buf.string()].emplace(file.string());
+        roots[buf].emplace(file.string());
 }
 
 static std::string quoteRegexChars(const std::string & raw)
@@ -466,7 +471,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
     {
         // The temp roots only store the hash part to make it easier to
         // ignore suffixes like '.lock', '.chroot' and '.check'.
-        boost::unordered_flat_set<std::string> tempRoots;
+        boost::unordered_flat_set<std::string, StringViewHash, std::equal_to<>> tempRoots;
 
         // Hash part of the store path currently being deleted, if
         // any.
@@ -575,9 +580,9 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
                             auto storePath = maybeParseStorePath(path);
                             if (storePath) {
                                 debug("got new GC root '%s'", path);
-                                auto hashPart = std::string(storePath->hashPart());
+                                auto hashPart = storePath->hashPart();
                                 auto shared(_shared.lock());
-                                shared->tempRoots.insert(hashPart);
+                                shared->tempRoots.emplace(hashPart);
                                 /* If this path is currently being
                                    deleted, then we have to wait until
                                    deletion is finished to ensure that
@@ -629,7 +634,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
     Roots tempRoots;
     findTempRoots(tempRoots, true);
     for (auto & root : tempRoots) {
-        _shared.lock()->tempRoots.insert(std::string(root.first.hashPart()));
+        _shared.lock()->tempRoots.emplace(root.first.hashPart());
         roots.insert(root.first);
     }
 
@@ -736,7 +741,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
                 return;
 
             {
-                auto hashPart = std::string(path->hashPart());
+                auto hashPart = path->hashPart();
                 auto shared(_shared.lock());
                 if (shared->tempRoots.count(hashPart)) {
                     debug("cannot delete '%s' because it's a temporary root", printStorePath(*path));
diff --git a/src/libstore/include/nix/store/gc-store.hh b/src/libstore/include/nix/store/gc-store.hh
index fba9d6079..5a4a6db14 100644
--- a/src/libstore/include/nix/store/gc-store.hh
+++ b/src/libstore/include/nix/store/gc-store.hh
@@ -7,7 +7,11 @@
 
 namespace nix {
 
-typedef boost::unordered_flat_map<StorePath, boost::unordered_flat_set<std::string>, std::hash<StorePath>> Roots;
+typedef boost::unordered_flat_map<
+    StorePath,
+    boost::unordered_flat_set<std::string, StringViewHash, std::equal_to<>>,
+    std::hash<StorePath>>
+    Roots;
 
 struct GCOptions
 {