diff --git a/config/src/main/java/com/typesafe/config/impl/ConfigParser.java b/config/src/main/java/com/typesafe/config/impl/ConfigParser.java
index cce541636..1e562ace2 100644
--- a/config/src/main/java/com/typesafe/config/impl/ConfigParser.java
+++ b/config/src/main/java/com/typesafe/config/impl/ConfigParser.java
@@ -59,7 +59,7 @@ private AbstractConfigValue parseConcatenation(ConfigNodeConcatenation n) {
             if (flavor == ConfigSyntax.JSON)
                 throw new ConfigException.BugOrBroken("Found a concatenation node in JSON");
 
-            List<AbstractConfigValue> values = new ArrayList<AbstractConfigValue>();
+            List<AbstractConfigValue> values = new ArrayList<AbstractConfigValue>(n.children().size());
 
             for (AbstractConfigNode node : n.children()) {
                 AbstractConfigValue v = null;
diff --git a/config/src/main/java/com/typesafe/config/impl/SimpleConfigOrigin.java b/config/src/main/java/com/typesafe/config/impl/SimpleConfigOrigin.java
index a3dc3e4d5..9e05f9e91 100644
--- a/config/src/main/java/com/typesafe/config/impl/SimpleConfigOrigin.java
+++ b/config/src/main/java/com/typesafe/config/impl/SimpleConfigOrigin.java
@@ -364,7 +364,7 @@ static ConfigOrigin mergeOrigins(Collection<? extends ConfigOrigin> stack) {
             Iterator<? extends ConfigOrigin> i = stack.iterator();
             return mergeTwo((SimpleConfigOrigin) i.next(), (SimpleConfigOrigin) i.next());
         } else {
-            List<SimpleConfigOrigin> remaining = new ArrayList<SimpleConfigOrigin>();
+            List<SimpleConfigOrigin> remaining = new ArrayList<SimpleConfigOrigin>(stack.size());
             for (ConfigOrigin o : stack) {
                 remaining.add((SimpleConfigOrigin) o);
             }