diff --git a/src/tinyexpr.cpp b/src/tinyexpr.cpp
index a3c03ca21..356ed90bb 100644
--- a/src/tinyexpr.cpp
+++ b/src/tinyexpr.cpp
@@ -65,6 +65,8 @@ public:
             default: arity = 0;
         }
 
+        parameters.reserve(arity);
+
         // We allow filling the parameters later.
         if (params) {
             for (int i = 0; i < arity; i++) parameters.push_back(params[i]);