diff --git a/operation.go b/operation.go
index 720d593..cea5051 100644
--- a/operation.go
+++ b/operation.go
@@ -8,6 +8,7 @@ import (
 	"github.com/oaswrap/spec/internal/debuglog"
 	specopenapi "github.com/oaswrap/spec/openapi"
 	"github.com/oaswrap/spec/option"
+	"github.com/swaggest/jsonschema-go"
 	"github.com/swaggest/openapi-go"
 	"github.com/swaggest/openapi-go/openapi3"
 	"github.com/swaggest/openapi-go/openapi31"
@@ -76,7 +77,7 @@ func (oc *operationContextImpl) build() openapi.OperationContext {
 		logger.LogOp(method, path, "add request", value)
 	}
 
-	for _, resp := range cfg.Responses {
+	for _, resp := range mergeResponses(cfg.Responses) {
 		opts, value := oc.buildResponseOpts(resp)
 		oc.op.AddRespStructure(resp.Structure, opts...)
 		logger.LogOp(method, path, "add response", value)
@@ -85,6 +86,60 @@ func (oc *operationContextImpl) build() openapi.OperationContext {
 	return oc.op
 }
 
+// responseKey identifies a unique response slot by HTTP status and content type.
+type responseKey struct {
+	httpStatus  int
+	contentType string
+}
+
+// mergeResponses groups responses by (HTTPStatus, ContentType) and combines
+// duplicates into a single response using jsonschema.OneOf.
+func mergeResponses(responses []*specopenapi.ContentUnit) []*specopenapi.ContentUnit {
+	if len(responses) <= 1 {
+		return responses
+	}
+
+	type group struct {
+		key   responseKey
+		items []*specopenapi.ContentUnit
+	}
+
+	var order []responseKey
+	groups := make(map[responseKey]*group)
+
+	for _, resp := range responses {
+		k := responseKey{httpStatus: resp.HTTPStatus, contentType: resp.ContentType}
+		g, exists := groups[k]
+		if !exists {
+			g = &group{key: k}
+			groups[k] = g
+			order = append(order, k)
+		}
+		g.items = append(g.items, resp)
+	}
+
+	result := make([]*specopenapi.ContentUnit, 0, len(order))
+	for _, k := range order {
+		g := groups[k]
+		if len(g.items) == 1 {
+			result = append(result, g.items[0])
+			continue
+		}
+
+		// Merge multiple structures into oneOf.
+		structures := make([]interface{}, 0, len(g.items))
+		for _, item := range g.items {
+			structures = append(structures, item.Structure)
+		}
+
+		merged := *g.items[0] // copy first entry for description, status, etc.
+		merged.Structure = jsonschema.OneOf(structures...)
+		result = append(result, &merged)
+	}
+
+	return result
+}
+
 func stringMapToEncodingMap3(enc map[string]string) map[string]openapi3.Encoding {
 	res := map[string]openapi3.Encoding{}
 	for k, v := range enc {
diff --git a/router_test.go b/router_test.go
index 69c81b1..191be70 100644
--- a/router_test.go
+++ b/router_test.go
@@ -606,6 +606,25 @@ func TestRouter(t *testing.T) {
 				)
 			},
 		},
+		{
+			name:   "Duplicate Status Code Responses",
+			golden: "duplicate_status_code_responses",
+			setup: func(r spec.Router) {
+				type SuccessA struct {
+					Message string `json:"message"`
+				}
+				type SuccessB struct {
+					Count int `json:"count"`
+				}
+				r.Get("/mixed",
+					option.OperationID("getMixed"),
+					option.Summary("Get Mixed Responses"),
+					option.Description("Returns one of two possible response shapes."),
+					option.Response(200, new(SuccessA)),
+					option.Response(200, new(SuccessB)),
+				)
+			},
+		},
 		{
 			name:   "Server Variables",
 			golden: "server_variables",
diff --git a/testdata/duplicate_status_code_responses_3.yaml b/testdata/duplicate_status_code_responses_3.yaml
new file mode 100644
index 0000000..8ca12d2
--- /dev/null
+++ b/testdata/duplicate_status_code_responses_3.yaml
@@ -0,0 +1,32 @@
+openapi: 3.0.3
+info:
+  description: This is the API documentation for Duplicate Status Code Responses
+  title: 'API Doc: Duplicate Status Code Responses'
+  version: 1.0.0
+paths:
+  /mixed:
+    get:
+      description: Returns one of two possible response shapes.
+      operationId: getMixed
+      responses:
+        "200":
+          content:
+            application/json:
+              schema:
+                oneOf:
+                - $ref: '#/components/schemas/SpecTestSuccessA'
+                - $ref: '#/components/schemas/SpecTestSuccessB'
+          description: OK
+      summary: Get Mixed Responses
+components:
+  schemas:
+    SpecTestSuccessA:
+      properties:
+        message:
+          type: string
+      type: object
+    SpecTestSuccessB:
+      properties:
+        count:
+          type: integer
+      type: object
diff --git a/testdata/duplicate_status_code_responses_31.yaml b/testdata/duplicate_status_code_responses_31.yaml
new file mode 100644
index 0000000..24c7670
--- /dev/null
+++ b/testdata/duplicate_status_code_responses_31.yaml
@@ -0,0 +1,32 @@
+openapi: 3.1.0
+info:
+  description: This is the API documentation for Duplicate Status Code Responses
+  title: 'API Doc: Duplicate Status Code Responses'
+  version: 1.0.0
+paths:
+  /mixed:
+    get:
+      description: Returns one of two possible response shapes.
+      operationId: getMixed
+      responses:
+        "200":
+          content:
+            application/json:
+              schema:
+                oneOf:
+                - $ref: '#/components/schemas/SpecTestSuccessA'
+                - $ref: '#/components/schemas/SpecTestSuccessB'
+          description: OK
+      summary: Get Mixed Responses
+components:
+  schemas:
+    SpecTestSuccessA:
+      properties:
+        message:
+          type: string
+      type: object
+    SpecTestSuccessB:
+      properties:
+        count:
+          type: integer
+      type: object