--- title: ASP.NET Core: Why I Couldn’t Upgrade FluentValidation... description: The author of the Calzolari.Grpc.AspNetCore.Validation package explains why upgrading FluentValidation past version 11.4 caused runtime crashes in ASP.NET Core... canonical: https://daily.dev/posts/asp-net-core-why-i-couldn-t-upgrade-fluentvalidation-past-11-4-in-my-calzolari-grpc-aspnetcore-vali-d0wccrjem twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: ASP.NET Core: Why I Couldn’t Upgrade FluentValidation Past 11.4 in My Calzolari.Grpc.AspNetCore.Validation Package (and How I Finally Fixed It) – Anthony Giretti's .NET blog | daily.dev og:description: The author of the Calzolari.Grpc.AspNetCore.Validation package explains why upgrading FluentValidation past version 11.4 caused runtime crashes in ASP.NET Core... og:url: https://daily.dev/posts/asp-net-core-why-i-couldn-t-upgrade-fluentvalidation-past-11-4-in-my-calzolari-grpc-aspnetcore-vali-d0wccrjem og:image: https://api.daily.dev/og/posts/d0WccrJEm.png og:image:alt: ASP.NET Core: Why I Couldn’t Upgrade FluentValidation Past 11.4 in My Calzolari.Grpc.AspNetCore.Validation Package (and How I Finally Fixed It) – Anthony Giretti's .NET blog og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # ASP.NET Core: Why I Couldn’t Upgrade FluentValidation Past 11.4 in My Calzolari.Grpc.AspNetCore.Validation Package (and How I Finally Fixed It) – Anthony Giretti's .NET blog **[We Are .NET](https://daily.dev/sources/wearedotnet)** · [@anthonygiretti](https://daily.dev/anthonygiretti) · 4 min read · 11 upvotes · 0 comments ## Summary The author of the Calzolari.Grpc.AspNetCore.Validation package explains why upgrading FluentValidation past version 11.4 caused runtime crashes in ASP.NET Core gRPC applications. The root cause was FluentValidation 11.5+ making the IValidator generic parameter contravariant (adding the 'in' keyword), which introduced new internal types that slipped through the package's name-based assembly scanning filter and got registered in the DI container as non-instantiable types. The fix involves five improvements to the AddValidators() method: excluding all types from the FluentValidation assembly itself, filtering out abstract classes, interfaces, and open generic types, adding try/catch around GetTypes() calls, and silently skipping irrelevant types instead of crashing. The updated package (version 10.1.0) is now available on NuGet. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [ASP.NET Core in .NET 10: Major Updates Across Blazor, APIs, and OpenAPI](https://daily.dev/posts/asp-net-core-in-net-10-major-updates-across-blazor-apis-and-openapi-pt3fiswfo) · InfoQ · 17 upvotes · 0 comments --- Tags: [#aspnet](https://daily.dev/tags/aspnet), [#dependency-injection](https://daily.dev/tags/dependency-injection), [#grpc](https://daily.dev/tags/grpc) [View this post on daily.dev](https://daily.dev/posts/asp-net-core-why-i-couldn-t-upgrade-fluentvalidation-past-11-4-in-my-calzolari-grpc-aspnetcore-vali-d0wccrjem) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"ASP.NET Core: Why I Couldn’t Upgrade FluentValidation Past 11.4 in My Calzolari.Grpc.AspNetCore.Validation Package (and How I Finally Fixed It) – Anthony Giretti's .NET blog","url":"https://daily.dev/posts/asp-net-core-why-i-couldn-t-upgrade-fluentvalidation-past-11-4-in-my-calzolari-grpc-aspnetcore-vali-d0wccrjem","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/asp-net-core-why-i-couldn-t-upgrade-fluentvalidation-past-11-4-in-my-calzolari-grpc-aspnetcore-vali-d0wccrjem"},"datePublished":"2026-04-08T02:19:26.050Z","dateModified":"2026-04-08T23:00:15.399Z","description":"The author of the Calzolari.Grpc.AspNetCore.Validation package explains why upgrading FluentValidation past version 11.4 caused runtime crashes in ASP.NET Core...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/7350b3bd1fcfd19ebfba5efad490134a?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/7350b3bd1fcfd19ebfba5efad490134a?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"We Are .NET","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Person","name":"Anthony Giretti","url":"https://daily.dev/anthonygiretti","image":"https://lh3.googleusercontent.com/a-/AOh14GiElPbBkb-30Kuu7doFGSleMqjoukyjoX2V17cI8g=s100","interactionStatistic":{"@type":"InteractionCounter","interactionType":{"@type":"EndorseAction"},"userInteractionCount":140}},"commentCount":0,"discussionUrl":"https://daily.dev/posts/asp-net-core-why-i-couldn-t-upgrade-fluentvalidation-past-11-4-in-my-calzolari-grpc-aspnetcore-vali-d0wccrjem","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":11},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"aspnet,dependency-injection,grpc","timeRequired":"PT4M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"We Are .NET","item":"https://daily.dev/sources/wearedotnet"},{"@type":"ListItem","position":3,"name":"ASP.NET Core: Why I Couldn’t Upgrade FluentValidation Past 11.4 in My Calzolari.Grpc.AspNetCore.Validation Package (and How I Finally Fixed It) – Anthony Giretti's .NET blog"}]} ```