diff --git a/src/TextServices.Search.Api/Features/Autocomplete/AutocompleteEndpoints.cs b/src/TextServices.Search.Api/Features/Autocomplete/AutocompleteEndpoints.cs
index 241c3dd..00c1004 100644
--- a/src/TextServices.Search.Api/Features/Autocomplete/AutocompleteEndpoints.cs
+++ b/src/TextServices.Search.Api/Features/Autocomplete/AutocompleteEndpoints.cs
@@ -14,8 +14,10 @@ internal static IEndpointRouteBuilder MapAutocompleteEndpoints(this IEndpointRou
             IOptions<SearchApiOptions> options,
             HttpContext ctx) =>
         {
+            if (string.IsNullOrWhiteSpace(q)) return Results.BadRequest();
+
             var resolved = EndpointHelpers.Resolve(options.Value, ctx, "autocomplete/v1/", id, q);
-            var result = await sender.Send(new AutocompleteRequest(id, q ?? string.Empty, resolved.SelfUrl));
+            var result = await sender.Send(new AutocompleteRequest(id, q, resolved.SelfUrl));
             if (result == null) return Results.NotFound();
             return Results.Json(result, contentType: "application/ld+json");
         });
@@ -26,8 +28,10 @@ internal static IEndpointRouteBuilder MapAutocompleteEndpoints(this IEndpointRou
             IOptions<SearchApiOptions> options,
             HttpContext ctx) =>
         {
+            if (string.IsNullOrWhiteSpace(q)) return Results.BadRequest();
+
             var resolved = EndpointHelpers.Resolve(options.Value, ctx, "autocomplete/v2/", id, q);
-            var result = await sender.Send(new AutocompleteV2Request(id, q ?? string.Empty, resolved.SelfUrl));
+            var result = await sender.Send(new AutocompleteV2Request(id, q, resolved.SelfUrl));
             if (result == null) return Results.NotFound();
             return Results.Json(result, contentType: "application/ld+json");
         });
diff --git a/src/TextServices.Search.Api/Features/Search/SearchEndpoints.cs b/src/TextServices.Search.Api/Features/Search/SearchEndpoints.cs
index 78045ef..9c9e6dd 100644
--- a/src/TextServices.Search.Api/Features/Search/SearchEndpoints.cs
+++ b/src/TextServices.Search.Api/Features/Search/SearchEndpoints.cs
@@ -14,8 +14,10 @@ internal static IEndpointRouteBuilder MapSearchEndpoints(this IEndpointRouteBuil
             IOptions<SearchApiOptions> options,
             HttpContext ctx) =>
         {
+            if (string.IsNullOrWhiteSpace(q)) return Results.BadRequest();
+
             var resolved = EndpointHelpers.Resolve(options.Value, ctx, "search/v1/", id, q);
-            var result = await sender.Send(new SearchRequest(id, q ?? string.Empty, resolved.SelfUrl, resolved.ResourceUrl));
+            var result = await sender.Send(new SearchRequest(id, q, resolved.SelfUrl, resolved.ResourceUrl));
             if (result == null) return Results.NotFound();
             result.Ignored = EndpointHelpers.GetIgnoredParams(ctx);
             return Results.Json(result, contentType: "application/ld+json");
@@ -27,8 +29,10 @@ internal static IEndpointRouteBuilder MapSearchEndpoints(this IEndpointRouteBuil
             IOptions<SearchApiOptions> options,
             HttpContext ctx) =>
         {
+            if (string.IsNullOrWhiteSpace(q)) return Results.BadRequest();
+
             var resolved = EndpointHelpers.Resolve(options.Value, ctx, "search/v2/", id, q);
-            var result = await sender.Send(new SearchV2Request(id, q ?? string.Empty, resolved.SelfUrl, resolved.ResourceUrl));
+            var result = await sender.Send(new SearchV2Request(id, q, resolved.SelfUrl, resolved.ResourceUrl));
             if (result == null) return Results.NotFound();
             result.Ignored = EndpointHelpers.GetIgnoredParams(ctx);
             return Results.Json(result, contentType: "application/ld+json");
diff --git a/src/TextServices.Tests.E2E/BuildAndSearchTests.cs b/src/TextServices.Tests.E2E/BuildAndSearchTests.cs
index b8fcc4a..a75a436 100644
--- a/src/TextServices.Tests.E2E/BuildAndSearchTests.cs
+++ b/src/TextServices.Tests.E2E/BuildAndSearchTests.cs
@@ -169,15 +169,11 @@ public async Task Search_KnownWord_ReturnsHits()
     }
 
     [Fact]
-    public async Task Search_EmptyQuery_ReturnsEmptyNotError()
+    public async Task Search_EmptyQuery_Returns400()
     {
-        var id = await BuildFixtureAsync("e2e/search-empty");
-
-        var response = await ctx.SearchClient.GetAsync($"/search/v1/{id}?q=");
-        response.StatusCode.ShouldBe(HttpStatusCode.OK);
-
-        var body = JsonNode.Parse(await response.Content.ReadAsStringAsync())!;
-        body["resources"]!.AsArray().Count.ShouldBe(0);
+        // Query validation happens before the job is looked up, so no fixture is needed.
+        var response = await ctx.SearchClient.GetAsync("/search/v1/no/such/id?q=");
+        response.StatusCode.ShouldBe(HttpStatusCode.BadRequest);
     }
 
     [Fact]
@@ -187,6 +183,15 @@ public async Task Search_UnknownId_Returns404()
         response.StatusCode.ShouldBe(HttpStatusCode.NotFound);
     }
 
+    [Fact]
+    public async Task Search_MissingQuery_Returns400EvenForUnknownId()
+    {
+        // Query validation happens before the job is looked up — an unknown id
+        // with a missing query returns 400, not 404.
+        var response = await ctx.SearchClient.GetAsync("/search/v2/no/such/id");
+        response.StatusCode.ShouldBe(HttpStatusCode.BadRequest);
+    }
+
     // -------------------------------------------------------------------------
     // Autocomplete API
     // -------------------------------------------------------------------------
@@ -204,6 +209,14 @@ public async Task Autocomplete_ShortQuery_ReturnsEmptyTermList()
         body["terms"]!.AsArray().Count.ShouldBe(0);
     }
 
+    [Fact]
+    public async Task Autocomplete_MissingQuery_Returns400()
+    {
+        // Query validation happens before the job is looked up, so no fixture is needed.
+        var response = await ctx.SearchClient.GetAsync("/autocomplete/v1/no/such/id");
+        response.StatusCode.ShouldBe(HttpStatusCode.BadRequest);
+    }
+
     [Fact]
     public async Task Autocomplete_MatchingPrefix_ReturnsSuggestions()
     {