diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index c73535bb73e..7eaf18a18ec 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -2014,7 +2014,7 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
         return result;
     };
 
-    boost::container::small_vector<Value, 64> values(es->size());
+    boost::container::small_vector<Value, 16> values(es->size());
     Value * vTmpP = values.data();
 
     for (auto & [i_pos, i] : *es) {
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index d104b7180d7..7aa2122819f 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -2549,7 +2549,7 @@ static void prim_removeAttrs(EvalState & state, const PosIdx pos, Value * * args
     /* Get the attribute names to be removed.
        We keep them as Attrs instead of Symbols so std::set_difference
        can be used to remove them from attrs[0]. */
-    boost::container::small_vector<Attr, 64> names;
+    boost::container::small_vector<Attr, 16> names;
     names.reserve(args[1]->listSize());
     for (auto elem : args[1]->listItems()) {
         state.forceStringNoCtx(*elem, pos, "while evaluating the values of the second argument passed to builtins.removeAttrs");
@@ -3452,7 +3452,7 @@ static void prim_concatMap(EvalState & state, const PosIdx pos, Value * * args,
     state.forceList(*args[1], pos, "while evaluating the second argument passed to builtins.concatMap");
     auto nrLists = args[1]->listSize();
 
-    boost::container::small_vector<Value, 64> lists(nrLists);
+    boost::container::small_vector<Value, 16> lists(nrLists);
     size_t len = 0;
 
     for (unsigned int n = 0; n < nrLists; ++n) {