diff --git a/Projects/UOContent.Tests/Tests/Accounting/Security/PasswordProtectionTest.cs b/Projects/UOContent.Tests/Tests/Accounting/Security/PasswordProtectionTest.cs
index 1a6e08f6f..a84557f7c 100644
--- a/Projects/UOContent.Tests/Tests/Accounting/Security/PasswordProtectionTest.cs
+++ b/Projects/UOContent.Tests/Tests/Accounting/Security/PasswordProtectionTest.cs
@@ -105,6 +105,21 @@ public class PasswordProtectionTest
         Assert.Equal(expected, Argon2PasswordProtection.Instance.NeedsRehash(hash));
     }
 
+    // The digest and salt lengths are not in the parameter list -- they are the decoded sizes of the
+    // two base64 segments -- so they cannot be varied through the theory template above. Both hashes
+    // here carry the current type and cost; only a segment length differs from the library defaults
+    // (32-byte digest, 16-byte salt). The "current defaults" row of the theory above is the negative
+    // control: it uses those default lengths and must stay false.
+    [Theory]
+    // 16-byte digest: 22 base64 chars instead of the 43 a 32-byte digest encodes to.
+    [InlineData("$argon2id$v=19$m=16384,t=1,p=1$LD1XJz7P3wQmIJ+Tu6ScgA$NO5hBABsHQ172C5nDO2X4g")]
+    // 8-byte salt: 11 base64 chars instead of the 22 a 16-byte salt encodes to.
+    [InlineData("$argon2id$v=19$m=16384,t=1,p=1$LD1XJz7P3wQ$NO5hBABsHQ172C5nDO2X4gWnB4jDef3x6WhLdVE2LFw")]
+    public void Argon2_NeedsRehash_ComparesSaltAndDigestLengths(string hash)
+    {
+        Assert.True(Argon2PasswordProtection.Instance.NeedsRehash(hash));
+    }
+
     [Theory]
     [InlineData("")]
     [InlineData("not-a-hash")]
diff --git a/Projects/UOContent/Accounting/Security/Argon2PasswordProtection.cs b/Projects/UOContent/Accounting/Security/Argon2PasswordProtection.cs
index f89150aa5..9f0221e43 100644
--- a/Projects/UOContent/Accounting/Security/Argon2PasswordProtection.cs
+++ b/Projects/UOContent/Accounting/Security/Argon2PasswordProtection.cs
@@ -23,9 +23,10 @@ public class Argon2PasswordProtection : IPasswordProtection
 
     // Argon2id over Argon2i: RFC 9106 recommends Argon2i only where side-channel resistance is
     // required and memory is scarce. 16 MiB at t=1 measures cheaper than the old 8 MiB at t=3
-    // (8.5 ms vs 10.1 ms) while doubling memory-hardness, which is the property that resists GPU
-    // and ASIC cracking; iterations mostly buy wall-clock. p=1 because native argon2 spawns a
-    // thread per lane, which is oversubscription on the 1-2 core hosts this path exists to serve.
+    // (8.5 ms vs 10.1 ms, measured by ModernUO-Benchmarks/Benchmarks/Argon2Hashing) while doubling
+    // memory-hardness, which is the property that resists GPU and ASIC cracking; iterations mostly
+    // buy wall-clock. p=1 because native argon2 spawns a thread per lane, which is oversubscription
+    // on the 1-2 core hosts this path exists to serve.
     private readonly Argon2PasswordHasher _passwordHasher = new(
         time: 1,
         memory: 16384,
@@ -52,9 +53,15 @@ public class Argon2PasswordProtection : IPasswordProtection
             return true;
         }
 
+        // The digest and salt lengths live in the base64 segments rather than the parameter list,
+        // but they are just as much a part of "was this produced with the parameters we configure
+        // today". Casting the hasher's uint properties keeps the comparison signed-vs-signed; both
+        // are small byte counts, so the narrowing cannot lose anything.
         return values.ArgonType != _passwordHasher.ArgonType
                || values.MemoryCost != _passwordHasher.MemoryCost
                || values.TimeCost != _passwordHasher.TimeCost
-               || values.Parallelism != _passwordHasher.Parallelism;
+               || values.Parallelism != _passwordHasher.Parallelism
+               || values.HashLength != (int)_passwordHasher.HashLength
+               || values.SaltLength != (int)_passwordHasher.SaltLength;
     }
 }