diff --git a/merge/src/ordered_merge.rs b/merge/src/ordered_merge.rs
index e9d71c8..a422fc9 100644
--- a/merge/src/ordered_merge.rs
+++ b/merge/src/ordered_merge.rs
@@ -18,7 +18,8 @@ pub fn ordered_merge<'a>(
         ));
     }
 
-    let mut result_children = vec![];
+    let mut result_children =
+        Vec::with_capacity(left.get_children().len() + right.get_children().len());
 
     let mut children_left_it = left.get_children().iter();
     let mut children_right_it = right.get_children().iter();
diff --git a/merge/src/unordered_merge.rs b/merge/src/unordered_merge.rs
index 07a3fc5..e675612 100644
--- a/merge/src/unordered_merge.rs
+++ b/merge/src/unordered_merge.rs
@@ -23,8 +23,9 @@ pub fn unordered_merge<'a>(
         ));
     }
 
-    let mut result_children = vec![];
-    let mut processed_nodes: HashSet<uuid::Uuid> = HashSet::new();
+    let max_capacity = left.get_children().len() + right.get_children().len();
+    let mut result_children = Vec::with_capacity(max_capacity);
+    let mut processed_nodes = HashSet::with_capacity(max_capacity);
 
     for left_child in left.get_children().iter() {
         if let CSTNode::Terminal(Terminal {