diff --git a/apps/api/internal/clients/clients_test.go b/apps/api/internal/clients/clients_test.go
index 700f6d9..7f528fb 100644
--- a/apps/api/internal/clients/clients_test.go
+++ b/apps/api/internal/clients/clients_test.go
@@ -1306,6 +1306,25 @@ func TestGeminiClientImageGenerateBuildsNativeImageBody(t *testing.T) {
 	}
 }
 
+func TestGeminiGenerationConfigInitializesMissingImageConfig(t *testing.T) {
+	config := geminiGenerationConfig(map[string]any{
+		"aspect_ratio": "16:9",
+		"resolution":   "4K",
+	}, true)
+
+	imageConfig, ok := config["imageConfig"].(map[string]any)
+	if !ok {
+		t.Fatalf("imageConfig should be initialized, got %+v", config)
+	}
+	if imageConfig["aspectRatio"] != "16:9" || imageConfig["imageSize"] != "4K" {
+		t.Fatalf("unexpected imageConfig: %+v", imageConfig)
+	}
+	modalities, ok := config["responseModalities"].([]any)
+	if !ok || len(modalities) != 1 || modalities[0] != "IMAGE" {
+		t.Fatalf("image response modality should be initialized, got %+v", config)
+	}
+}
+
 func TestGeminiClientImageEditPreservesNativeContentsAndFileData(t *testing.T) {
 	var captured map[string]any
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
diff --git a/apps/api/internal/clients/gemini.go b/apps/api/internal/clients/gemini.go
index 8cfe74f..6dc86bc 100644
--- a/apps/api/internal/clients/gemini.go
+++ b/apps/api/internal/clients/gemini.go
@@ -195,14 +195,23 @@ func geminiApplyRequestOptions(body map[string]any, request Request, imageRespon
 func geminiGenerationConfig(body map[string]any, imageResponse bool) map[string]any {
 	source := mapFromAny(firstPresent(body["generationConfig"], body["generation_config"]))
 	out := cloneMapAny(source)
+	if out == nil {
+		out = map[string]any{}
+	}
 	if aspectRatio := firstNonEmptyString(body["aspect_ratio"], body["aspectRatio"]); aspectRatio != "" {
 		imageConfig := cloneMapAny(mapFromAny(firstPresent(out["imageConfig"], out["image_config"])))
+		if imageConfig == nil {
+			imageConfig = map[string]any{}
+		}
 		imageConfig["aspectRatio"] = aspectRatio
 		out["imageConfig"] = imageConfig
 		delete(out, "image_config")
 	}
 	if imageSize := firstNonEmptyString(body["resolution"], body["imageSize"], body["image_size"], body["size"]); imageSize != "" {
 		imageConfig := cloneMapAny(mapFromAny(firstPresent(out["imageConfig"], out["image_config"])))
+		if imageConfig == nil {
+			imageConfig = map[string]any{}
+		}
 		imageConfig["imageSize"] = imageSize
 		out["imageConfig"] = imageConfig
 		delete(out, "image_config")