diff --git a/spring-core/src/main/java/org/springframework/util/MimeTypeUtils.java b/spring-core/src/main/java/org/springframework/util/MimeTypeUtils.java
index b97877970c42..6b99b5bc13f5 100644
--- a/spring-core/src/main/java/org/springframework/util/MimeTypeUtils.java
+++ b/spring-core/src/main/java/org/springframework/util/MimeTypeUtils.java
@@ -23,8 +23,8 @@
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Iterator;
-import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Random;
 import java.util.function.BiPredicate;
@@ -437,7 +437,9 @@ private void resolveBareType(String candidate) {
 
 		private void putParameter(String name, String value) {
 			if (this.parameters == null) {
-				this.parameters = new LinkedHashMap<>(4);
+				// Parameter names are case-insensitive, so use a case-insensitive
+				// map in order to reject duplicates that differ only in case.
+				this.parameters = new LinkedCaseInsensitiveMap<>(4, Locale.ROOT);
 			}
 			if (this.parameters.put(name, value) != null) {
 				throw new InvalidMimeTypeException(this.input, "duplicate parameter '" + name + "=" + value + "'");
diff --git a/spring-core/src/test/java/org/springframework/util/MimeTypeTests.java b/spring-core/src/test/java/org/springframework/util/MimeTypeTests.java
index bef9ebfde422..fa4327520f03 100644
--- a/spring-core/src/test/java/org/springframework/util/MimeTypeTests.java
+++ b/spring-core/src/test/java/org/springframework/util/MimeTypeTests.java
@@ -174,6 +174,12 @@ void valueOfDuplicateParameter() {
 					.hasMessageContaining("Invalid mime type \"text/plain;dupe=\"1\";dupe=\"2\"\": duplicate parameter 'dupe=\"2\"'");
 		}
 
+		@Test
+		void valueOfDuplicateParameterWithDifferentCase() {
+			assertThatThrownBy(() -> MimeType.valueOf("text/plain;dupe=\"1\";DUPE=\"2\"")).isInstanceOf(InvalidMimeTypeException.class)
+					.hasMessageContaining("Invalid mime type \"text/plain;dupe=\"1\";DUPE=\"2\"\": duplicate parameter 'DUPE=\"2\"'");
+		}
+
 	}