diff --git a/oauth2/oauth2-resource-server/src/main/java/org/springframework/security/oauth2/server/resource/web/server/ServerBearerTokenAuthenticationConverter.java b/oauth2/oauth2-resource-server/src/main/java/org/springframework/security/oauth2/server/resource/web/server/ServerBearerTokenAuthenticationConverter.java
index 0c712f0b93..d59c943e6c 100644
--- a/oauth2/oauth2-resource-server/src/main/java/org/springframework/security/oauth2/server/resource/web/server/ServerBearerTokenAuthenticationConverter.java
+++ b/oauth2/oauth2-resource-server/src/main/java/org/springframework/security/oauth2/server/resource/web/server/ServerBearerTokenAuthenticationConverter.java
@@ -53,7 +53,7 @@ public class ServerBearerTokenAuthenticationConverter
 	private String bearerTokenHeaderName = HttpHeaders.AUTHORIZATION;
 
 	public Mono<Authentication> convert(ServerWebExchange exchange) {
-		return Mono.justOrEmpty(token(exchange.getRequest()))
+		return Mono.fromCallable(() -> token(exchange.getRequest()))
 			.map(token -> {
 				if (token.isEmpty()) {
 					BearerTokenError error = invalidTokenError();
diff --git a/oauth2/oauth2-resource-server/src/test/java/org/springframework/security/oauth2/server/resource/web/server/ServerBearerTokenAuthenticationConverterTests.java b/oauth2/oauth2-resource-server/src/test/java/org/springframework/security/oauth2/server/resource/web/server/ServerBearerTokenAuthenticationConverterTests.java
index c35c344580..e7932d6f66 100644
--- a/oauth2/oauth2-resource-server/src/test/java/org/springframework/security/oauth2/server/resource/web/server/ServerBearerTokenAuthenticationConverterTests.java
+++ b/oauth2/oauth2-resource-server/src/test/java/org/springframework/security/oauth2/server/resource/web/server/ServerBearerTokenAuthenticationConverterTests.java
@@ -142,6 +142,17 @@ public class ServerBearerTokenAuthenticationConverterTests {
 				.hasMessageContaining(("Bearer token is malformed"));
 	}
 
+	// gh-8865
+	@Test
+	public void resolveWhenHeaderWithInvalidCharactersIsPresentAndNotSubscribedThenNoneExceptionIsThrown() {
+		MockServerHttpRequest.BaseBuilder<?> request = MockServerHttpRequest
+				.get("/")
+				.header(HttpHeaders.AUTHORIZATION, "Bearer an\"invalid\"token");
+
+		assertThatCode(() -> this.converter.convert(MockServerWebExchange.from(request)))
+				.doesNotThrowAnyException();
+	}
+
 	@Test
 	public void resolveWhenValidHeaderIsPresentTogetherWithQueryParameterThenAuthenticationExceptionIsThrown() {
 		MockServerHttpRequest.BaseBuilder<?> request = MockServerHttpRequest