diff --git a/protoc-gen-openapiv2/internal/genopenapi/generator_test.go b/protoc-gen-openapiv2/internal/genopenapi/generator_test.go
index 18e755f266e..1255d7ae5cb 100644
--- a/protoc-gen-openapiv2/internal/genopenapi/generator_test.go
+++ b/protoc-gen-openapiv2/internal/genopenapi/generator_test.go
@@ -2075,135 +2075,3 @@ func TestIssue5684_UnusedMethodsNotInOpenAPI(t *testing.T) {
 		t.Errorf("expected exactly 1 path, got %d paths", len(paths))
 	}
 }
-
-// TestGenerateMergeFilesWithBodyAndPathParams tests that OpenAPI generation
-// doesn't panic when merging files where a service uses body:"*" with path parameters.
-// This reproduces the bug from https://github.com/grpc-ecosystem/grpc-gateway/issues/6274
-func TestGenerateMergeFilesWithBodyAndPathParams(t *testing.T) {
-	t.Parallel()
-
-	// First proto file: contains only message definitions, with swagger option
-	// This file will be the merge target since it has the swagger option
-	const messagesProto = `
-	proto_file: {
-		name: "example/v1/messages.proto"
-		package: "example.v1"
-		message_type: {
-			name: "Item"
-			field: {
-				name: "id"
-				number: 1
-				label: LABEL_OPTIONAL
-				type: TYPE_STRING
-				json_name: "id"
-			}
-			field: {
-				name: "name"
-				number: 2
-				label: LABEL_OPTIONAL
-				type: TYPE_STRING
-				json_name: "name"
-			}
-		}
-		message_type: {
-			name: "UpdateItemRequest"
-			field: {
-				name: "id"
-				number: 1
-				label: LABEL_OPTIONAL
-				type: TYPE_STRING
-				json_name: "id"
-			}
-			field: {
-				name: "name"
-				number: 2
-				label: LABEL_OPTIONAL
-				type: TYPE_STRING
-				json_name: "name"
-			}
-		}
-		options: {
-			go_package: "example/v1;examplev1"
-			[grpc.gateway.protoc_gen_openapiv2.options.openapiv2_swagger]: {
-				info: {
-					title: "Test API"
-					version: "1.0"
-				}
-			}
-		}
-		syntax: "proto3"
-	}`
-
-	// Second proto file: contains the service that references messages from first file
-	// This file does NOT have the swagger option, so it won't be the merge target
-	const serviceProto = `
-	proto_file: {
-		name: "example/v1/service.proto"
-		package: "example.v1"
-		dependency: "example/v1/messages.proto"
-		service: {
-			name: "ItemService"
-			method: {
-				name: "UpdateItem"
-				input_type: ".example.v1.UpdateItemRequest"
-				output_type: ".example.v1.Item"
-				options: {
-					[google.api.http]: {
-						put: "/v1/items/{id}"
-						body: "*"
-					}
-				}
-			}
-		}
-		options: {
-			go_package: "example/v1;examplev1"
-		}
-		syntax: "proto3"
-	}`
-
-	var msgReq, svcReq pluginpb.CodeGeneratorRequest
-	if err := prototext.Unmarshal([]byte(messagesProto), &msgReq); err != nil {
-		t.Fatalf("failed to unmarshal messages proto: %s", err)
-	}
-	if err := prototext.Unmarshal([]byte(serviceProto), &svcReq); err != nil {
-		t.Fatalf("failed to unmarshal service proto: %s", err)
-	}
-
-	// Combine into a single request with both files to generate
-	req := &pluginpb.CodeGeneratorRequest{
-		ProtoFile:      append(msgReq.ProtoFile, svcReq.ProtoFile...),
-		FileToGenerate: []string{"example/v1/messages.proto", "example/v1/service.proto"},
-	}
-
-	formats := [...]genopenapi.Format{
-		genopenapi.FormatJSON,
-		genopenapi.FormatYAML,
-	}
-
-	for _, format := range formats {
-		format := format
-		t.Run(string(format), func(t *testing.T) {
-			t.Parallel()
-
-			// This should not panic - the bug causes panic with
-			// "failed to resolve method FQN: '.example.v1.ItemService.UpdateItem'"
-			resp := requireGenerate(t, req, format, false, true)
-			if len(resp) != 1 {
-				t.Fatalf("invalid count, expected: 1, actual: %d", len(resp))
-			}
-
-			content := resp[0].GetContent()
-			t.Log(content)
-
-			// Verify the path exists in output
-			if !strings.Contains(content, "/v1/items/{id}") {
-				t.Error("expected /v1/items/{id} path in output")
-			}
-
-			// Verify the body definition was created (this is what triggers the bug)
-			if !strings.Contains(content, "ItemServiceUpdateItemBody") {
-				t.Error("expected ItemServiceUpdateItemBody definition in output")
-			}
-		})
-	}
-}
diff --git a/protoc-gen-openapiv2/internal/genopenapi/template.go b/protoc-gen-openapiv2/internal/genopenapi/template.go
index 224f60659aa..a1635f5dce2 100644
--- a/protoc-gen-openapiv2/internal/genopenapi/template.go
+++ b/protoc-gen-openapiv2/internal/genopenapi/template.go
@@ -1569,14 +1569,7 @@ func renderServices(services []*descriptor.Service, paths *openapiPathsObject, r
 								if meth.Name != nil {
 									methFQN, ok := fullyQualifiedNameToOpenAPIName(meth.FQMN(), reg)
 									if !ok {
-										// Fallback: use FQN naming (strip leading dot) if method FQN not found in mapping.
-										// This can happen when files are merged and method FQNs are not properly registered.
-										fqmn := meth.FQMN()
-										if len(fqmn) > 0 && fqmn[0] == '.' {
-											methFQN = fqmn[1:]
-										} else {
-											methFQN = fqmn
-										}
+										panic(fmt.Errorf("failed to resolve method FQN: '%s'", meth.FQMN()))
 									}
 									defName := methFQN + "Body"
 									schema.Ref = fmt.Sprintf("#/definitions/%s", defName)
@@ -2085,15 +2078,6 @@ func operationForMethod(httpMethod string) func(*openapiPathItemObject) *openapi
 
 // This function is called with a param which contains the entire definition of a method.
 func applyTemplate(p param) (*openapiSwaggerObject, error) {
-	// Clear the naming cache for this registry at the start of each file processing.
-	// This is necessary because when multiple files are processed, the cache may contain
-	// a filtered mapping from a previous file that doesn't include all names needed
-	// for the current file (e.g., method FQNs from the current file's services).
-	// The cache will be rebuilt with the appropriate filtered names later in this function.
-	registriesSeenMutex.Lock()
-	delete(registriesSeen, p.reg)
-	registriesSeenMutex.Unlock()
-
 	// Create the basic template object. This is the object that everything is
 	// defined off of.
 	s := openapiSwaggerObject{