diff --git a/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/authentication/OpenSaml4AuthenticationProvider.java b/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/authentication/OpenSaml4AuthenticationProvider.java
index 59f2585596..13987df902 100644
--- a/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/authentication/OpenSaml4AuthenticationProvider.java
+++ b/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/authentication/OpenSaml4AuthenticationProvider.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -391,7 +391,7 @@ public final class OpenSaml4AuthenticationProvider implements AuthenticationProv
 			String inResponseTo = response.getInResponseTo();
 			result = result.concat(validateInResponseTo(token.getAuthenticationRequest(), inResponseTo));
 
-			String issuer = response.getIssuer().getValue();
+			String issuer = issuer(response);
 			String destination = response.getDestination();
 			String location = token.getRelyingPartyRegistration().getAssertionConsumerServiceLocation();
 			if (StringUtils.hasText(destination) && !destination.equals(location)) {
@@ -414,6 +414,13 @@ public final class OpenSaml4AuthenticationProvider implements AuthenticationProv
 		};
 	}
 
+	private static String issuer(Response response) {
+		if (response.getIssuer() == null) {
+			return null;
+		}
+		return response.getIssuer().getValue();
+	}
+
 	private static List<String> getStatusCodes(Response response) {
 		if (response.getStatus() == null) {
 			return List.of(StatusCode.SUCCESS);
@@ -576,7 +583,7 @@ public final class OpenSaml4AuthenticationProvider implements AuthenticationProv
 	}
 
 	private void process(Saml2AuthenticationToken token, Response response) {
-		String issuer = response.getIssuer().getValue();
+		String issuer = issuer(response);
 		this.logger.debug(LogMessage.format("Processing SAML response from %s", issuer));
 		boolean responseSigned = response.isSigned();
 
diff --git a/saml2/saml2-service-provider/src/test/java/org/springframework/security/saml2/provider/service/authentication/OpenSaml4AuthenticationProviderTests.java b/saml2/saml2-service-provider/src/test/java/org/springframework/security/saml2/provider/service/authentication/OpenSaml4AuthenticationProviderTests.java
index abe4a4549a..bb3e61519b 100644
--- a/saml2/saml2-service-provider/src/test/java/org/springframework/security/saml2/provider/service/authentication/OpenSaml4AuthenticationProviderTests.java
+++ b/saml2/saml2-service-provider/src/test/java/org/springframework/security/saml2/provider/service/authentication/OpenSaml4AuthenticationProviderTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -861,6 +861,15 @@ public class OpenSaml4AuthenticationProviderTests {
 		provider.authenticate(token);
 	}
 
+	// gh-16989
+	@Test
+	public void authenticateWhenNullIssuerThenNoNullPointer() {
+		OpenSaml4AuthenticationProvider provider = new OpenSaml4AuthenticationProvider();
+		Response response = TestOpenSamlObjects.signedResponseWithOneAssertion((r) -> r.setIssuer(null));
+		Saml2AuthenticationToken token = token(response, verifying(registration()));
+		assertThatExceptionOfType(Saml2AuthenticationException.class).isThrownBy(() -> provider.authenticate(token));
+	}
+
 	private <T extends XMLObject> T build(QName qName) {
 		return (T) XMLObjectProviderRegistrySupport.getBuilderFactory().getBuilder(qName).buildObject(qName);
 	}