diff --git a/spring-kafka/src/main/java/org/springframework/kafka/annotation/KafkaListenerAnnotationBeanPostProcessor.java b/spring-kafka/src/main/java/org/springframework/kafka/annotation/KafkaListenerAnnotationBeanPostProcessor.java
index 00a0889cef..e4bca3a91e 100644
--- a/spring-kafka/src/main/java/org/springframework/kafka/annotation/KafkaListenerAnnotationBeanPostProcessor.java
+++ b/spring-kafka/src/main/java/org/springframework/kafka/annotation/KafkaListenerAnnotationBeanPostProcessor.java
@@ -30,6 +30,7 @@
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Properties;
 import java.util.Set;
@@ -1014,7 +1015,7 @@ else if (resolvedValue instanceof Integer intgr) {
 	private TopicPartitionOffset.SeekPosition resloveTopicPartitionOffsetSeekPosition(@Nullable Object seekPosition) {
 		TopicPartitionOffset.SeekPosition resloveTpoSp = null;
 		if (seekPosition instanceof String seekPositionName) {
-			String capitalLetterSeekPositionName = seekPositionName.trim().toUpperCase();
+			String capitalLetterSeekPositionName = seekPositionName.trim().toUpperCase(Locale.ROOT);
 			if (SeekPosition.BEGINNING.name().equals(capitalLetterSeekPositionName)) {
 				resloveTpoSp = SeekPosition.BEGINNING;
 			}
diff --git a/spring-kafka/src/main/java/org/springframework/kafka/support/AbstractKafkaHeaderMapper.java b/spring-kafka/src/main/java/org/springframework/kafka/support/AbstractKafkaHeaderMapper.java
index 03f655b299..186a2f78b9 100644
--- a/spring-kafka/src/main/java/org/springframework/kafka/support/AbstractKafkaHeaderMapper.java
+++ b/spring-kafka/src/main/java/org/springframework/kafka/support/AbstractKafkaHeaderMapper.java
@@ -24,6 +24,7 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.stream.Collectors;
@@ -351,13 +352,13 @@ protected SimplePatternBasedHeaderMatcher(String pattern) {
 
 		SimplePatternBasedHeaderMatcher(String pattern, boolean negate) {
 			Assert.notNull(pattern, "Pattern must no be null");
-			this.pattern = pattern.toLowerCase();
+			this.pattern = pattern.toLowerCase(Locale.ROOT);
 			this.negate = negate;
 		}
 
 		@Override
 		public boolean matchHeader(String headerName) {
-			String header = headerName.toLowerCase();
+			String header = headerName.toLowerCase(Locale.ROOT);
 			if (PatternMatchUtils.simpleMatch(this.pattern, header)) {
 				LOGGER.debug(() ->
 						MessageFormat.format(