diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 93e88d038..1447ab07c 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -1998,7 +1998,7 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
         } else if (firstType == nPath) {
             if (!first) {
                 auto part = state.coerceToString(i_pos, *vTmp, context, false, false);
-                if (sSize <= 1 && !hasPrefix(*part, "/"))
+                if (sSize <= 1 && !hasPrefix(*part, "/") && accessor != state.rootFS.get_ptr())
                     state.throwEvalError(i_pos,
                         "cannot append non-absolute path '%1%' to '%2%' (hint: change it to '/%1%')",
                         (std::string) *part, accessor->root().to_string(),