diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index e370e278c..f7dc16948 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -593,7 +593,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         auto path = store->parseStorePath(readString(from));
         logger->startWork();
         SubstitutablePathInfos infos;
-        store->querySubstitutablePathInfos({path}, infos);
+        store->querySubstitutablePathInfos({{path, std::nullopt}}, infos);
         logger->stopWork();
         auto i = infos.find(path);
         if (i == infos.end())
@@ -612,7 +612,10 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         auto paths = readStorePaths<StorePathSet>(*store, from);
         logger->startWork();
         SubstitutablePathInfos infos;
-        store->querySubstitutablePathInfos(paths, infos);
+        StorePathCAMap pathsMap = {};
+        for (auto & path : paths)
+            pathsMap.emplace(path, std::nullopt);
+        store->querySubstitutablePathInfos(pathsMap, infos);
         logger->stopWork();
         to << infos.size();
         for (auto & i : infos) {
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 3230312c9..3901d532a 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -841,22 +841,20 @@ StorePathSet LocalStore::querySubstitutablePaths(const StorePathSet & paths)
 }
 
 
-void LocalStore::querySubstitutablePathInfos(const StorePathSet & paths,
-    SubstitutablePathInfos & infos, std::map<std::string, std::string> pathsCA)
+void LocalStore::querySubstitutablePathInfos(const StorePathCAMap & paths, SubstitutablePathInfos & infos)
 {
     if (!settings.useSubstitutes) return;
     for (auto & sub : getDefaultSubstituters()) {
         for (auto & path : paths) {
-            auto subPath(path);
+            auto subPath(path.first);
 
-            auto ca = pathsCA.find(printStorePath(path));
             // recompute store path so that we can use a different store root
-            if (ca != pathsCA.end() && (hasPrefix(ca->second, "fixed:") || hasPrefix(ca->second, "text:"))) {
-                subPath = makeFixedOutputPathFromCA(path.name(), ca->second);
+            if (path.second && (hasPrefix(*path.second, "fixed:") || hasPrefix(*path.second, "text:"))) {
+                subPath = makeFixedOutputPathFromCA(path.first.name(), *path.second);
                 if (sub->storeDir == storeDir)
-                    assert(subPath == path);
-                if (subPath != path)
-                    debug("replaced path '%s' with '%s' for substituter '%s'", printStorePath(path), sub->printStorePath(subPath), sub->getUri());
+                    assert(subPath == path.first);
+                if (subPath != path.first)
+                    debug("replaced path '%s' with '%s' for substituter '%s'", printStorePath(path.first), sub->printStorePath(subPath), sub->getUri());
             } else if (sub->storeDir != storeDir) continue;
 
             debug("checking substituter '%s' for path '%s'", sub->getUri(), sub->printStorePath(subPath));
@@ -868,7 +866,7 @@ void LocalStore::querySubstitutablePathInfos(const StorePathSet & paths,
 
                 auto narInfo = std::dynamic_pointer_cast<const NarInfo>(
                     std::shared_ptr<const ValidPathInfo>(info));
-                infos.insert_or_assign(path, SubstitutablePathInfo{
+                infos.insert_or_assign(path.first, SubstitutablePathInfo{
                     info->deriver,
                     info->references,
                     narInfo ? narInfo->fileSize : 0,
diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
index 183d27c80..ab9fbfbe4 100644
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -139,9 +139,8 @@ public:
 
     StorePathSet querySubstitutablePaths(const StorePathSet & paths) override;
 
-    void querySubstitutablePathInfos(const StorePathSet & paths,
-        SubstitutablePathInfos & infos,
-        std::map<std::string, std::string> pathsCA = {}) override;
+    void querySubstitutablePathInfos(const StorePathCAMap & paths,
+        SubstitutablePathInfos & infos) override;
 
     void addToStore(const ValidPathInfo & info, Source & source,
         RepairFlag repair, CheckSigsFlag checkSigs,
diff --git a/src/libstore/misc.cc b/src/libstore/misc.cc
index 6902dfa0c..dc991e227 100644
--- a/src/libstore/misc.cc
+++ b/src/libstore/misc.cc
@@ -178,10 +178,7 @@ void Store::queryMissing(const std::vector<StorePathWithOutputs> & targets,
         auto outPath = parseStorePath(outPathS);
 
         SubstitutablePathInfos infos;
-        std::map<std::string, std::string> pathsCA = {};
-        if (auto ca = getDerivationCA(*drv))
-            pathsCA.insert({outPathS, *ca});
-        querySubstitutablePathInfos({outPath}, infos, pathsCA);
+        querySubstitutablePathInfos({{outPath, getDerivationCA(*drv)}}, infos);
 
         if (infos.empty()) {
             drvState_->lock()->done = true;
@@ -238,7 +235,7 @@ void Store::queryMissing(const std::vector<StorePathWithOutputs> & targets,
             if (isValidPath(path.path)) return;
 
             SubstitutablePathInfos infos;
-            querySubstitutablePathInfos({path.path}, infos);
+            querySubstitutablePathInfos({{path.path, std::nullopt}}, infos);
 
             if (infos.empty()) {
                 auto state(state_.lock());
diff --git a/src/libstore/path.hh b/src/libstore/path.hh
index aaebd3ec3..91962d114 100644
--- a/src/libstore/path.hh
+++ b/src/libstore/path.hh
@@ -62,6 +62,8 @@ public:
 typedef std::set<StorePath> StorePathSet;
 typedef std::vector<StorePath> StorePaths;
 
+typedef std::map<StorePath, std::optional<std::string>> StorePathCAMap;
+
 /* Extension of derivations in the Nix store. */
 const std::string drvExtension = ".drv";
 
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 396629a32..4538ccd4f 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -308,18 +308,17 @@ StorePathSet RemoteStore::querySubstitutablePaths(const StorePathSet & paths)
 }
 
 
-void RemoteStore::querySubstitutablePathInfos(const StorePathSet & paths,
-    SubstitutablePathInfos & infos, std::map<std::string, std::string> pathsCA)
+void RemoteStore::querySubstitutablePathInfos(const StorePathCAMap & pathsMap, SubstitutablePathInfos & infos)
 {
-    if (paths.empty()) return;
+    if (pathsMap.empty()) return;
 
     auto conn(getConnection());
 
     if (GET_PROTOCOL_MINOR(conn->daemonVersion) < 12) {
 
-        for (auto & i : paths) {
+        for (auto & i : pathsMap) {
             SubstitutablePathInfo info;
-            conn->to << wopQuerySubstitutablePathInfo << printStorePath(i);
+            conn->to << wopQuerySubstitutablePathInfo << printStorePath(i.first);
             conn.processStderr();
             unsigned int reply = readInt(conn->from);
             if (reply == 0) continue;
@@ -329,12 +328,15 @@ void RemoteStore::querySubstitutablePathInfos(const StorePathSet & paths,
             info.references = readStorePaths<StorePathSet>(*this, conn->from);
             info.downloadSize = readLongLong(conn->from);
             info.narSize = readLongLong(conn->from);
-            infos.insert_or_assign(i, std::move(info));
+            infos.insert_or_assign(i.first, std::move(info));
         }
 
     } else {
 
         conn->to << wopQuerySubstitutablePathInfos;
+        StorePathSet paths;
+        for (auto & path : pathsMap)
+            paths.insert(path.first);
         writeStorePaths(*this, conn->to, paths);
         conn.processStderr();
         size_t count = readNum<size_t>(conn->from);
diff --git a/src/libstore/remote-store.hh b/src/libstore/remote-store.hh
index 498a5c6a0..07ed2b51a 100644
--- a/src/libstore/remote-store.hh
+++ b/src/libstore/remote-store.hh
@@ -55,8 +55,8 @@ public:
 
     StorePathSet querySubstitutablePaths(const StorePathSet & paths) override;
 
-    void querySubstitutablePathInfos(const StorePathSet & paths,
-        SubstitutablePathInfos & infos, std::map<std::string, std::string> pathsCA = {}) override;
+    void querySubstitutablePathInfos(const StorePathCAMap & paths,
+        SubstitutablePathInfos & infos) override;
 
     void addToStore(const ValidPathInfo & info, Source & nar,
         RepairFlag repair, CheckSigsFlag checkSigs,
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 65954574f..12a6b6939 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -445,8 +445,8 @@ public:
     /* Query substitute info (i.e. references, derivers and download
        sizes) of a set of paths.  If a path does not have substitute
        info, it's omitted from the resulting ‘infos’ map. */
-    virtual void querySubstitutablePathInfos(const StorePathSet & paths,
-        SubstitutablePathInfos & infos, std::map<std::string, std::string> pathsCA = {}) { return; };
+    virtual void querySubstitutablePathInfos(const StorePathCAMap & paths,
+        SubstitutablePathInfos & infos) { return; };
 
     /* Import a path into the store. */
     virtual void addToStore(const ValidPathInfo & info, Source & narSource,