diff --git a/merlin-server/src/main/java/gov/nasa/jpl/aerie/merlin/server/http/ResponseSerializers.java b/merlin-server/src/main/java/gov/nasa/jpl/aerie/merlin/server/http/ResponseSerializers.java
index 82589af52b..b592f621da 100644
--- a/merlin-server/src/main/java/gov/nasa/jpl/aerie/merlin/server/http/ResponseSerializers.java
+++ b/merlin-server/src/main/java/gov/nasa/jpl/aerie/merlin/server/http/ResponseSerializers.java
@@ -189,12 +189,12 @@ public static JsonValue serializeBulkArgumentValidationResponse(BulkArgumentVali
       return Json.createObjectBuilder(serializeInstantiationException(f.ex()).asJsonObject())
           .add("type", "INSTANTIATION_ERRORS")
           .build();
-    } else if (response instanceof BulkArgumentValidationResponse.RuntimeError e) {
+    } else if (response instanceof BulkArgumentValidationResponse.RuntimeException e) {
       return Json.createObjectBuilder()
                  .add("success", JsonValue.FALSE)
                  .add("type", "RUNTIME_EXCEPTION")
-                 .add("errors", Json.createArrayBuilder()
-                     .add(e.t().getMessage())
+                 .add("errors", Json.createObjectBuilder()
+                     .add("runtimeException", e.t().getMessage())
                      .build())
                  .build();
     }
@@ -202,8 +202,8 @@ public static JsonValue serializeBulkArgumentValidationResponse(BulkArgumentVali
     // This should never happen, but we don't have exhaustive pattern matching
     return Json.createObjectBuilder()
                .add("success", JsonValue.FALSE)
-               .add("errors", Json.createArrayBuilder()
-                     .add(String.format("Internal error: %s", response))
+               .add("errors", Json.createObjectBuilder()
+                     .add("internalError", response.toString())
                      .build())
                .build();
   }
diff --git a/merlin-server/src/main/java/gov/nasa/jpl/aerie/merlin/server/services/LocalMissionModelService.java b/merlin-server/src/main/java/gov/nasa/jpl/aerie/merlin/server/services/LocalMissionModelService.java
index 12b319a285..2c74003875 100644
--- a/merlin-server/src/main/java/gov/nasa/jpl/aerie/merlin/server/services/LocalMissionModelService.java
+++ b/merlin-server/src/main/java/gov/nasa/jpl/aerie/merlin/server/services/LocalMissionModelService.java
@@ -165,7 +165,7 @@ public List<BulkArgumentValidationResponse> validateActivityArgumentsBulk(
       } catch (InstantiationException e) {
         return new BulkArgumentValidationResponse.InstantiationError(e);
       } catch (Throwable t) {
-        return new BulkArgumentValidationResponse.RuntimeError(t);
+        return new BulkArgumentValidationResponse.RuntimeException(t);
       }
     }).collect(Collectors.toList());
   }
diff --git a/merlin-server/src/main/java/gov/nasa/jpl/aerie/merlin/server/services/MissionModelService.java b/merlin-server/src/main/java/gov/nasa/jpl/aerie/merlin/server/services/MissionModelService.java
index 2e179be570..029c90675d 100644
--- a/merlin-server/src/main/java/gov/nasa/jpl/aerie/merlin/server/services/MissionModelService.java
+++ b/merlin-server/src/main/java/gov/nasa/jpl/aerie/merlin/server/services/MissionModelService.java
@@ -109,6 +109,6 @@ record Success() implements BulkArgumentValidationResponse { }
     record Validation(List<ValidationNotice> notices) implements BulkArgumentValidationResponse { }
     record NoSuchActivityError(NoSuchActivityTypeException ex) implements BulkArgumentValidationResponse { }
     record InstantiationError(InstantiationException ex) implements BulkArgumentValidationResponse { }
-    record RuntimeError(Throwable t) implements BulkArgumentValidationResponse { }
+    record RuntimeException(Throwable t) implements BulkArgumentValidationResponse { }
   }
 }