diff --git a/src/Bifrost.Web/Features/Heimdall/HeimdallIdentityMoveClient.cs b/src/Bifrost.Web/Features/Heimdall/HeimdallIdentityMoveClient.cs
index e485b37..f285ae2 100644
--- a/src/Bifrost.Web/Features/Heimdall/HeimdallIdentityMoveClient.cs
+++ b/src/Bifrost.Web/Features/Heimdall/HeimdallIdentityMoveClient.cs
@@ -33,7 +33,7 @@ public enum HeimdallProofTier
 public sealed record HeimdallMoveReceipt(
     string MoveId, string AccountId, IReadOnlyList<string> MovedIdentityIds, HeimdallProofTier ProofFrom, HeimdallProofTier? ProofTo, string? ReversesMoveId);
 
-/// <summary>Heimdall's fixed refusal codes for a move, plus the one local class: Heimdall's schema 400.</summary>
+/// <summary>Heimdall's fixed refusal codes for a move, plus invalid_request, Heimdall's own schema 400.</summary>
 public enum HeimdallMoveRefusal
 {
     AppAuthRequired,
@@ -128,12 +128,6 @@ public sealed partial class HeimdallIdentityMoveClient(
                 return new HeimdallMoveOutcome.Unknown($"HTTP {status}");
             }
 
-            // Fastify's schema 400 answers before the route runs, so it carries no Heimdall code and applied nothing.
-            if (status == 400)
-            {
-                return new HeimdallMoveOutcome.Refused(HeimdallMoveRefusal.RequestInvalid);
-            }
-
             return Refused(await HeimdallRefusal.ReadAsync(response, token), status);
         }
         catch (Exception) when (!cancellationToken.IsCancellationRequested)
@@ -144,7 +138,7 @@ public sealed partial class HeimdallIdentityMoveClient(
     }
 
     /// <summary>
-    /// Refused only for the coded refusals Heimdall's move route emits (4fe367a moveIdentitiesRoute). A 4xx without one of those codes
+    /// Refused only for the coded refusals Heimdall's move route emits (4fe367a moveIdentitiesRoute, and its error handler's invalid_request 400). A 4xx without one of those codes
     /// (a gateway's HTML 404, a 408, a code a later Heimdall adds) proves nothing was applied, so it is Unknown. move_id_conflict is
     /// Unknown too: a committed move answers it when its proofs no longer verify.
     /// </summary>
@@ -167,6 +161,8 @@ public sealed partial class HeimdallIdentityMoveClient(
             "already_moved" => HeimdallMoveRefusal.AlreadyMoved,
             "provider_conflict" => HeimdallMoveRefusal.ProviderConflict,
             "identity_not_found" => HeimdallMoveRefusal.IdentityNotFound,
+            // Heimdall's error handler gives its own 400 this code; an nginx or other edge 400 has none, so it is not Heimdall's refusal.
+            "invalid_request" when status == 400 => HeimdallMoveRefusal.RequestInvalid,
             _ => (HeimdallMoveRefusal?)null
         };
         if (code is not { } known)
diff --git a/tests/Bifrost.Web.Tests/FakeHeimdallMoverTests.cs b/tests/Bifrost.Web.Tests/FakeHeimdallMoverTests.cs
index b49c8be..c856c8f 100644
--- a/tests/Bifrost.Web.Tests/FakeHeimdallMoverTests.cs
+++ b/tests/Bifrost.Web.Tests/FakeHeimdallMoverTests.cs
@@ -71,7 +71,7 @@ public sealed class FakeHeimdallMoverTests
         };
         foreach (var json in bad)
         {
-            Assert.Equal(HttpStatusCode.BadRequest, (await Post(host, json)).Status);
+            Assert.Equal((HttpStatusCode.BadRequest, "invalid_request"), await Post(host, json));
         }
 
         Assert.Single(moves.Stored);
diff --git a/tests/Bifrost.Web.Tests/HeimdallIdentityMoveClientTests.cs b/tests/Bifrost.Web.Tests/HeimdallIdentityMoveClientTests.cs
index 8055c6d..a2cc873 100644
--- a/tests/Bifrost.Web.Tests/HeimdallIdentityMoveClientTests.cs
+++ b/tests/Bifrost.Web.Tests/HeimdallIdentityMoveClientTests.cs
@@ -292,7 +292,7 @@ public sealed class HeimdallIdentityMoveClientTests
     }
 
     [Fact]
-    public async Task A_400_is_RequestInvalid_a_definitive_refusal_that_moves_nothing()
+    public async Task A_400_carrying_Heimdalls_invalid_request_code_is_RequestInvalid_a_definitive_refusal_that_moves_nothing()
     {
         using var host = new HeimdallHost();
         var moves = host.Heimdall.Moves;
@@ -307,6 +307,11 @@ public sealed class HeimdallIdentityMoveClientTests
     [Theory]
     [InlineData(HttpStatusCode.NotFound, "<html><body>404 Not Found</body></html>")]
     [InlineData(HttpStatusCode.NotFound, "")]
+    [InlineData(HttpStatusCode.BadRequest, "<html><head><title>400 Bad Request</title></head><body>nginx</body></html>")]
+    [InlineData(HttpStatusCode.BadRequest, "")]
+    [InlineData(HttpStatusCode.BadRequest, """{"statusCode":400,"error":"Bad Request","message":"x"}""")]
+    [InlineData(HttpStatusCode.BadRequest, """{"message":"no error field"}""")]
+    [InlineData(HttpStatusCode.Conflict, """{"error":"invalid_request"}""")]
     [InlineData(HttpStatusCode.RequestTimeout, "")]
     [InlineData(HttpStatusCode.RequestTimeout, """{"error":"request_timeout"}""")]
     [InlineData(HttpStatusCode.Gone, "")]
diff --git a/tests/Bifrost.Web.Tests/Support/FakeMoves.cs b/tests/Bifrost.Web.Tests/Support/FakeMoves.cs
index ef3eb35..1a87171 100644
--- a/tests/Bifrost.Web.Tests/Support/FakeMoves.cs
+++ b/tests/Bifrost.Web.Tests/Support/FakeMoves.cs
@@ -102,7 +102,7 @@ public sealed class FakeMoves(Func<DateTimeOffset> now)
 
         if (Parse(body) is not { } move)
         {
-            return Json(HttpStatusCode.BadRequest, """{"statusCode":400,"error":"Bad Request","message":"body does not match the schema"}""");
+            return Json(HttpStatusCode.BadRequest, """{"error":"invalid_request","detail":"body: must match the schema"}""");
         }
 
         if (MoveStatus is { } forced)
@@ -110,7 +110,7 @@ public sealed class FakeMoves(Func<DateTimeOffset> now)
             return forced == HttpStatusCode.NotFound
                 ? new HttpResponseMessage(forced)
                 : Json(forced, forced == HttpStatusCode.BadRequest
-                    ? """{"statusCode":400,"error":"Bad Request"}"""
+                    ? """{"error":"invalid_request","detail":"body: must match the schema"}"""
                     : """{"error":"server_error","detail":"HEIMDALL FREE TEXT"}""");
         }