diff --git a/src/libexpr/include/nix/expr/nixexpr.hh b/src/libexpr/include/nix/expr/nixexpr.hh
index fd7ed2a6745..afaf50b2b11 100644
--- a/src/libexpr/include/nix/expr/nixexpr.hh
+++ b/src/libexpr/include/nix/expr/nixexpr.hh
@@ -760,11 +760,19 @@ struct ExprConcatStrings : Expr
 {
     PosIdx pos;
     bool forceString;
-    std::vector<std::pair<PosIdx, Expr *>> es;
-    ExprConcatStrings(const PosIdx & pos, bool forceString, std::vector<std::pair<PosIdx, Expr *>> && es)
+    std::span<std::pair<PosIdx, Expr *>> es;
+
+    ExprConcatStrings(
+        std::pmr::polymorphic_allocator<char> & alloc,
+        const PosIdx & pos,
+        bool forceString,
+        const std::vector<std::pair<PosIdx, Expr *>> & es)
         : pos(pos)
         , forceString(forceString)
-        , es(std::move(es)) {};
+        , es({alloc.allocate_object<std::pair<PosIdx, Expr *>>(es.size()), es.size()})
+    {
+        std::ranges::copy(es, this->es.begin());
+    };
 
     PosIdx getPos() const override
     {
diff --git a/src/libexpr/include/nix/expr/parser-state.hh b/src/libexpr/include/nix/expr/parser-state.hh
index 4cffaa49779..e303b81ce5c 100644
--- a/src/libexpr/include/nix/expr/parser-state.hh
+++ b/src/libexpr/include/nix/expr/parser-state.hh
@@ -341,7 +341,7 @@ ParserState::stripIndentation(const PosIdx pos, std::vector<std::pair<PosIdx, st
         auto * const result = (es2)[0].second;
         return result;
     }
-    return new ExprConcatStrings(pos, true, std::move(es2));
+    return new ExprConcatStrings(alloc, pos, true, std::move(es2));
 }
 
 inline PosIdx LexerState::at(const ParserLocation & loc)
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index 29586ed989b..e695b7679f5 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -253,7 +253,7 @@ expr_op
   | expr_op UPDATE expr_op { $$ = new ExprOpUpdate(state->at(@2), $1, $3); }
   | expr_op '?' attrpath { $$ = new ExprOpHasAttr(state->alloc, $1, std::move($3)); }
   | expr_op '+' expr_op
-    { $$ = new ExprConcatStrings(state->at(@2), false, {{state->at(@1), $1}, {state->at(@3), $3}}); }
+    { $$ = new ExprConcatStrings(state->alloc, state->at(@2), false, {{state->at(@1), $1}, {state->at(@3), $3}}); }
   | expr_op '-' expr_op { $$ = new ExprCall(state->at(@2), new ExprVar(state->s.sub), {$1, $3}); }
   | expr_op '*' expr_op { $$ = new ExprCall(state->at(@2), new ExprVar(state->s.mul), {$1, $3}); }
   | expr_op '/' expr_op { $$ = new ExprCall(state->at(@2), new ExprVar(state->s.div), {$1, $3}); }
@@ -309,7 +309,7 @@ expr_simple
   | path_start PATH_END
   | path_start string_parts_interpolated PATH_END {
       $2.insert($2.begin(), {state->at(@1), $1});
-      $$ = new ExprConcatStrings(CUR_POS, false, std::move($2));
+      $$ = new ExprConcatStrings(state->alloc, CUR_POS, false, std::move($2));
   }
   | SPATH {
       std::string_view path($1.p + 1, $1.l - 2);
@@ -343,7 +343,7 @@ expr_simple
 
 string_parts
   : STR { $$ = $1; }
-  | string_parts_interpolated { $$ = new ExprConcatStrings(CUR_POS, true, std::move($1)); }
+  | string_parts_interpolated { $$ = new ExprConcatStrings(state->alloc, CUR_POS, true, std::move($1)); }
   | { $$ = std::string_view(); }
   ;