diff --git a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/ServerProperties.java b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/ServerProperties.java
index 508fac0bbef..027551b6c7a 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/ServerProperties.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/ServerProperties.java
@@ -409,6 +409,11 @@ public class ServerProperties {
 		 */
 		private Duration connectionTimeout;
 
+		/**
+		 * Whether to reject requests with illegal header names or values.
+		 */
+		private boolean rejectIllegalHeader = true;
+
 		/**
 		 * Static resource configuration.
 		 */
@@ -424,11 +429,6 @@ public class ServerProperties {
 		 */
 		private final Remoteip remoteip = new Remoteip();
 
-		/**
-		 * reject illegal header setting.
-		 */
-		private Boolean rejectIllegalHeader;
-
 		public DataSize getMaxHttpFormPostSize() {
 			return this.maxHttpFormPostSize;
 		}
@@ -565,6 +565,14 @@ public class ServerProperties {
 			this.connectionTimeout = connectionTimeout;
 		}
 
+		public boolean isRejectIllegalHeader() {
+			return this.rejectIllegalHeader;
+		}
+
+		public void setRejectIllegalHeader(boolean rejectIllegalHeader) {
+			this.rejectIllegalHeader = rejectIllegalHeader;
+		}
+
 		public Resource getResource() {
 			return this.resource;
 		}
@@ -577,14 +585,6 @@ public class ServerProperties {
 			return this.remoteip;
 		}
 
-		public Boolean getRejectIllegalHeader() {
-			return this.rejectIllegalHeader;
-		}
-
-		public void setRejectIllegalHeader(Boolean rejectIllegalHeader) {
-			this.rejectIllegalHeader = rejectIllegalHeader;
-		}
-
 		/**
 		 * Tomcat access log properties.
 		 */
diff --git a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/embedded/TomcatWebServerFactoryCustomizer.java b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/embedded/TomcatWebServerFactoryCustomizer.java
index 1545a3c879e..b55d2d9a66f 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/embedded/TomcatWebServerFactoryCustomizer.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/embedded/TomcatWebServerFactoryCustomizer.java
@@ -117,7 +117,7 @@ public class TomcatWebServerFactoryCustomizer
 				.to((relaxedChars) -> customizeRelaxedPathChars(factory, relaxedChars));
 		propertyMapper.from(tomcatProperties::getRelaxedQueryChars).as(this::joinCharacters).whenHasText()
 				.to((relaxedChars) -> customizeRelaxedQueryChars(factory, relaxedChars));
-		propertyMapper.from(tomcatProperties::getRejectIllegalHeader).whenNonNull()
+		propertyMapper.from(tomcatProperties::isRejectIllegalHeader)
 				.to((rejectIllegalHeader) -> customizeRejectIllegalHeader(factory, rejectIllegalHeader));
 		customizeStaticResources(factory);
 		customizeErrorReportValve(properties.getError(), factory);
diff --git a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/ServerPropertiesTests.java b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/ServerPropertiesTests.java
index ec551783eb6..6234688ebc5 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/ServerPropertiesTests.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/ServerPropertiesTests.java
@@ -130,7 +130,7 @@ class ServerPropertiesTests {
 		map.put("server.tomcat.remoteip.protocol-header", "X-Forwarded-Protocol");
 		map.put("server.tomcat.remoteip.remote-ip-header", "Remote-Ip");
 		map.put("server.tomcat.remoteip.internal-proxies", "10\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}");
-		map.put("server.tomcat.reject-illegal-header", "true");
+		map.put("server.tomcat.reject-illegal-header", "false");
 		map.put("server.tomcat.background-processor-delay", "10");
 		map.put("server.tomcat.relaxed-path-chars", "|,<");
 		map.put("server.tomcat.relaxed-query-chars", "^  ,  | ");
@@ -153,7 +153,7 @@ class ServerPropertiesTests {
 		assertThat(tomcat.getRemoteip().getRemoteIpHeader()).isEqualTo("Remote-Ip");
 		assertThat(tomcat.getRemoteip().getProtocolHeader()).isEqualTo("X-Forwarded-Protocol");
 		assertThat(tomcat.getRemoteip().getInternalProxies()).isEqualTo("10\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}");
-		assertThat(tomcat.getRejectIllegalHeader()).isTrue();
+		assertThat(tomcat.isRejectIllegalHeader()).isFalse();
 		assertThat(tomcat.getBackgroundProcessorDelay()).hasSeconds(10);
 		assertThat(tomcat.getRelaxedPathChars()).containsExactly('|', '<');
 		assertThat(tomcat.getRelaxedQueryChars()).containsExactly('^', '|');
@@ -408,8 +408,9 @@ class ServerPropertiesTests {
 	}
 
 	@Test
-	void tomcatRejectIllegalHeaderDefaultsToNull() {
-		assertThat(this.properties.getTomcat().getRejectIllegalHeader()).isNull();
+	void tomcatRejectIllegalHeaderMatchesProtocolDefault() throws Exception {
+		assertThat(getDefaultProtocol()).hasFieldOrPropertyWithValue("rejectIllegalHeader",
+				this.properties.getTomcat().isRejectIllegalHeader());
 	}
 
 	@Test