diff --git a/src/libstore/download.cc b/src/libstore/download.cc
index 6eb870966..4d7f56901 100644
--- a/src/libstore/download.cc
+++ b/src/libstore/download.cc
@@ -632,7 +632,7 @@ Path Downloader::downloadCached(ref<Store> store, const string & url_, bool unpa
     if (expectedHash) {
         expectedStorePath = store->makeFixedOutputPath(unpack, expectedHash, name);
         if (store->isValidPath(expectedStorePath))
-            return expectedStorePath;
+            return store->toRealPath(expectedStorePath);
     }
 
     Path cacheDir = getCacheDir() + "/nix/tarballs";
@@ -726,8 +726,13 @@ Path Downloader::downloadCached(ref<Store> store, const string & url_, bool unpa
         storePath = unpackedStorePath;
     }
 
-    if (expectedStorePath != "" && storePath != expectedStorePath)
-        throw nix::Error("store path mismatch in file downloaded from '%s'", url);
+    if (expectedStorePath != "" && storePath != expectedStorePath) {
+        Hash gotHash = unpack
+            ? hashPath(expectedHash.type, store->toRealPath(storePath)).first
+            : hashFile(expectedHash.type, store->toRealPath(storePath));
+        throw nix::Error("hash mismatch in file downloaded from '%s': expected hash '%s', got '%s'",
+            url, expectedHash.to_string(), gotHash.to_string());
+    }
 
     return store->toRealPath(storePath);
 }