diff --git a/cmd/protoc-gen-openapi/examples/tests/additional_bindings/openapi.yaml b/cmd/protoc-gen-openapi/examples/tests/additional_bindings/openapi.yaml
index 15c32d3e..41ce71ae 100644
--- a/cmd/protoc-gen-openapi/examples/tests/additional_bindings/openapi.yaml
+++ b/cmd/protoc-gen-openapi/examples/tests/additional_bindings/openapi.yaml
@@ -10,7 +10,7 @@ paths:
         patch:
             tags:
                 - Messaging
-            operationId: Messaging_UpdateMessage
+            operationId: Messaging_UpdateMessage_2
             requestBody:
                 content:
                     application/json:
diff --git a/cmd/protoc-gen-openapi/generator/generator.go b/cmd/protoc-gen-openapi/generator/generator.go
index 03907e26..a07ef07f 100644
--- a/cmd/protoc-gen-openapi/generator/generator.go
+++ b/cmd/protoc-gen-openapi/generator/generator.go
@@ -737,7 +737,7 @@ func (g *OpenAPIv3Generator) addPathsToDocumentV3(d *v3.Document, services []*pr
 				rules = append(rules, rule.AdditionalBindings...)
 			}
 
-			for _, rule := range rules {
+			for i, rule := range rules {
 				var path string
 				var methodName string
 				var reqBody string
@@ -768,10 +768,15 @@ func (g *OpenAPIv3Generator) addPathsToDocumentV3(d *v3.Document, services []*pr
 				}
 
 				if methodName != "" {
+					opID := operationID
+					if i > 0 {
+						// operationId must be unique (OpenAPI v3.0.3 4.7.10.1)
+						opID = fmt.Sprintf("%s_%d", operationID, i+1)
+					}
 					defaultHost := proto.GetExtension(service.Desc.Options(), annotations.E_DefaultHost).(string)
 
 					op, path2 := g.buildOperationV3(
-						d, operationID, service.GoName, comment, defaultHost, path, reqBody, resBody, inputMessage, outputMessage)
+						d, opID, service.GoName, comment, defaultHost, path, reqBody, resBody, inputMessage, outputMessage)
 
 					// Merge any `Operation` annotations with the current
 					extOperation := proto.GetExtension(method.Desc.Options(), v3.E_Operation)