diff --git a/crypto/src/main/java/org/springframework/security/crypto/argon2/Argon2EncodingUtils.java b/crypto/src/main/java/org/springframework/security/crypto/argon2/Argon2EncodingUtils.java
index 4b27d90318a..9f06c8bb245 100644
--- a/crypto/src/main/java/org/springframework/security/crypto/argon2/Argon2EncodingUtils.java
+++ b/crypto/src/main/java/org/springframework/security/crypto/argon2/Argon2EncodingUtils.java
@@ -111,7 +111,7 @@ static Argon2Hash decode(String encodedHash) throws IllegalArgumentException {
 			case "argon2d" -> new Argon2Parameters.Builder(Argon2Parameters.ARGON2_d);
 			case "argon2i" -> new Argon2Parameters.Builder(Argon2Parameters.ARGON2_i);
 			case "argon2id" -> new Argon2Parameters.Builder(Argon2Parameters.ARGON2_id);
-			default -> throw new IllegalArgumentException("Invalid algorithm type: " + parts[0]);
+			default -> throw new IllegalArgumentException("Invalid algorithm type: " + parts[1]);
 		};
 		if (parts[currentPart].startsWith("v=")) {
 			paramsBuilder.withVersion(Integer.parseInt(parts[currentPart].substring(2)));
diff --git a/crypto/src/test/java/org/springframework/security/crypto/argon2/Argon2EncodingUtilsTests.java b/crypto/src/test/java/org/springframework/security/crypto/argon2/Argon2EncodingUtilsTests.java
index abae39532f9..265527e71e1 100644
--- a/crypto/src/test/java/org/springframework/security/crypto/argon2/Argon2EncodingUtilsTests.java
+++ b/crypto/src/test/java/org/springframework/security/crypto/argon2/Argon2EncodingUtilsTests.java
@@ -94,8 +94,10 @@ public void decodeWhenNotAnArgon2HashThenThrowException() {
 
 	@Test
 	public void decodeWhenNonexistingAlgorithmThenThrowException() {
-		assertThatIllegalArgumentException().isThrownBy(() -> Argon2EncodingUtils
-			.decode("$argon2x$v=19$m=1024,t=3,p=2$Y1JkRmJDdzIzZ3oyTWx4aw$cGE5Cbd/cx7micVhXVBdH5qTr66JI1iUyuNNVAnErXs"));
+		assertThatIllegalArgumentException()
+			.isThrownBy(() -> Argon2EncodingUtils.decode(
+					"$argon2x$v=19$m=1024,t=3,p=2$Y1JkRmJDdzIzZ3oyTWx4aw$cGE5Cbd/cx7micVhXVBdH5qTr66JI1iUyuNNVAnErXs"))
+			.withMessageContaining("argon2x");
 	}
 
 	@Test