diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 084ccbee2..29d109ac4 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -2250,7 +2250,7 @@ BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet
         if (canonicalizePath)
             path = canonPath(*path);
         if (copyToStore)
-            path = copyPathToStore(context, std::move(path).toOwned());
+            path = store->printStorePath(copyPathToStore(context, std::move(path).toOwned()));
         return path;
     }
 
@@ -2293,26 +2293,26 @@ BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet
 }
 
 
-std::string EvalState::copyPathToStore(PathSet & context, const Path & path)
+StorePath EvalState::copyPathToStore(PathSet & context, const Path & path)
 {
     if (nix::isDerivation(path))
         throwEvalError("file names are not allowed to end in '%1%'", drvExtension);
 
-    Path dstPath;
-    auto i = srcToStore.find(path);
-    if (i != srcToStore.end())
-        dstPath = store->printStorePath(i->second);
-    else {
-        auto p = settings.readOnlyMode
+    auto dstPath = [&]() -> StorePath
+    {
+        auto i = srcToStore.find(path);
+        if (i != srcToStore.end()) return i->second;
+
+        auto dstPath = settings.readOnlyMode
             ? store->computeStorePathForPath(std::string(baseNameOf(path)), checkSourcePath(path)).first
             : store->addToStore(std::string(baseNameOf(path)), checkSourcePath(path), FileIngestionMethod::Recursive, htSHA256, defaultPathFilter, repair);
-        dstPath = store->printStorePath(p);
-        allowPath(p);
-        srcToStore.insert_or_assign(path, std::move(p));
-        printMsg(lvlChatty, "copied source '%1%' -> '%2%'", path, dstPath);
-    }
+        allowPath(dstPath);
+        srcToStore.insert_or_assign(path, dstPath);
+        printMsg(lvlChatty, "copied source '%1%' -> '%2%'", path, store->printStorePath(dstPath));
+        return dstPath;
+    }();
 
-    context.insert(dstPath);
+    context.insert(store->printStorePath(dstPath));
     return dstPath;
 }
 
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 21666339b..52b1736fe 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -400,7 +400,7 @@ public:
         bool coerceMore = false, bool copyToStore = true,
         bool canonicalizePath = true);
 
-    std::string copyPathToStore(PathSet & context, const Path & path);
+    StorePath copyPathToStore(PathSet & context, const Path & path);
 
     /* Path coercion.  Converts strings, paths and derivations to a
        path.  The result is guaranteed to be a canonicalised, absolute
diff --git a/src/libexpr/value-to-json.cc b/src/libexpr/value-to-json.cc
index 5dc453b2e..c35c876e3 100644
--- a/src/libexpr/value-to-json.cc
+++ b/src/libexpr/value-to-json.cc
@@ -1,6 +1,7 @@
 #include "value-to-json.hh"
 #include "eval-inline.hh"
 #include "util.hh"
+#include "store-api.hh"
 
 #include <cstdlib>
 #include <iomanip>
@@ -35,7 +36,7 @@ json printValueAsJSON(EvalState & state, bool strict,
 
         case nPath:
             if (copyToStore)
-                out = state.copyPathToStore(context, v.path);
+                out = state.store->printStorePath(state.copyPathToStore(context, v.path));
             else
                 out = v.path;
             break;