diff --git a/lix/libstore/store-api.cc b/lix/libstore/store-api.cc
index 910451a84..53d9b1117 100644
--- a/lix/libstore/store-api.cc
+++ b/lix/libstore/store-api.cc
@@ -401,12 +401,12 @@ struct RetrieveRegularNARVisitor : NARParseVisitor
 
     box_ptr<NARParseVisitor> createDirectory(const std::string & name) override
     {
-        assert(false && "RetrieveRegularNARVisitor::createDirectory must not be called");
+        throw Error("cannot import directory using flat ingestion");
     }
 
     void createSymlink(const std::string & name, const std::string & target) override
     {
-        assert(false && "RetrieveRegularNARVisitor::createSymlink must not be called");
+        throw Error("cannot import symlink using flat ingestion");
     }
 };
 }
diff --git a/tests/functional/add.sh b/tests/functional/add.sh
index 5c3eed793..38ce9d2d9 100644
--- a/tests/functional/add.sh
+++ b/tests/functional/add.sh
@@ -1,5 +1,11 @@
 source common.sh
 
+expectStderr 1 nix-store --add-fixed sha256 . | grep "cannot import directory using flat ingestion"
+expectStderr 1 nix-store --add-fixed sha256 ./symlink | grep "cannot import symlink using flat ingestion"
+
+expectStderr 1 nix-store --add-fixed sha1 . | grep "cannot import directory using flat ingestion"
+expectStderr 1 nix-store --add-fixed sha1 ./symlink | grep "cannot import symlink using flat ingestion"
+
 path1=$(nix-store --add ./dummy)
 echo $path1
 
diff --git a/tests/functional/symlink b/tests/functional/symlink
new file mode 120000
index 000000000..429f42921
--- /dev/null
+++ b/tests/functional/symlink
@@ -0,0 +1 @@
+add.sh
\ No newline at end of file