diff --git a/spring-context/src/main/java/org/springframework/context/support/StaticMessageSource.java b/spring-context/src/main/java/org/springframework/context/support/StaticMessageSource.java
index 26df79d7b711..bdd0f087b3ef 100644
--- a/spring-context/src/main/java/org/springframework/context/support/StaticMessageSource.java
+++ b/spring-context/src/main/java/org/springframework/context/support/StaticMessageSource.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,7 +17,9 @@
 package org.springframework.context.support;
 
 import java.text.MessageFormat;
+import java.util.Arrays;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Locale;
 import java.util.Map;
 
@@ -37,20 +39,20 @@
 public class StaticMessageSource extends AbstractMessageSource {
 
 	/** Map from 'code + locale' keys to message Strings. */
-	private final Map<String, String> messages = new HashMap<>();
+	private final Map<List<?>, String> messages = new HashMap<>();
 
-	private final Map<String, MessageFormat> cachedMessageFormats = new HashMap<>();
+	private final Map<List<?>, MessageFormat> cachedMessageFormats = new HashMap<>();
 
 
 	@Override
 	protected String resolveCodeWithoutArguments(String code, Locale locale) {
-		return this.messages.get(code + '_' + locale.toString());
+		return this.messages.get(Arrays.asList(code, locale));
 	}
 
 	@Override
 	@Nullable
 	protected MessageFormat resolveCode(String code, Locale locale) {
-		String key = code + '_' + locale.toString();
+		List<?> key = Arrays.asList(code, locale);
 		String msg = this.messages.get(key);
 		if (msg == null) {
 			return null;
@@ -75,7 +77,7 @@ public void addMessage(String code, Locale locale, String msg) {
 		Assert.notNull(code, "Code must not be null");
 		Assert.notNull(locale, "Locale must not be null");
 		Assert.notNull(msg, "Message must not be null");
-		this.messages.put(code + '_' + locale.toString(), msg);
+		this.messages.put(Arrays.asList(code, locale), msg);
 		if (logger.isDebugEnabled()) {
 			logger.debug("Added message [" + msg + "] for code [" + code + "] and Locale [" + locale + "]");
 		}