diff --git a/src/Eval.cpp b/src/Eval.cpp
index e96464576..97f0c5ad8 100644
--- a/src/Eval.cpp
+++ b/src/Eval.cpp
@@ -224,6 +224,8 @@ void Eval::evaluatePostfixStack (
 
   // This is stack used by the postfix evaluator.
   std::vector <Variant> values;
+  values.reserve(tokens.size());
+
   for (const auto& token : tokens)
   {
     // Unary operators.