diff --git a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/StandardStackTracePrinterTests.java b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/StandardStackTracePrinterTests.java
index 3cd1012860..3150f15787 100644
--- a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/StandardStackTracePrinterTests.java
+++ b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/StandardStackTracePrinterTests.java
@@ -263,8 +263,7 @@ class StandardStackTracePrinterTests {
 	void withLineSeparatorUsesLineSeparator() {
 		Throwable exception = TestException.create();
 		StandardStackTracePrinter printer = StandardStackTracePrinter.rootLast().withLineSeparator("!");
-		assertThatCleanedStackTraceMatches(printer, exception,
-				standardStackTrace().replace(System.lineSeparator(), "!"));
+		assertThatCleanedStackTraceMatches(printer, exception, standardStackTrace().replace("\n", "!"));
 	}
 
 	@Test
diff --git a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/structured/StructuredLoggingJsonPropertiesTests.java b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/structured/StructuredLoggingJsonPropertiesTests.java
index 7b3a370c50..7bd10b42f1 100644
--- a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/structured/StructuredLoggingJsonPropertiesTests.java
+++ b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/structured/StructuredLoggingJsonPropertiesTests.java
@@ -144,7 +144,8 @@ class StructuredLoggingJsonPropertiesTests {
 		void createPrinterWhenStandardAppliesCustomizations() {
 			Exception exception = TestException.create();
 			StackTrace properties = new StackTrace(null, Root.FIRST, 300, 2, true, false);
-			StackTracePrinter printer = properties.createPrinter();
+			StackTracePrinter printer = ((StandardStackTracePrinter) properties.createPrinter())
+				.withLineSeparator("\n");
 			String actual = TestException.withoutLineNumbers(printer.printStackTraceToString(exception));
 			assertThat(actual).isEqualToNormalizingNewlines("""
 					java.lang.RuntimeException: exception