diff --git a/rest/.jvm/src/test/resources/RestTestApi.json b/rest/.jvm/src/test/resources/RestTestApi.json
index e0c98d5b0..8f7e08210 100644
--- a/rest/.jvm/src/test/resources/RestTestApi.json
+++ b/rest/.jvm/src/test/resources/RestTestApi.json
@@ -267,6 +267,56 @@
         }
       }
     },
+    "/groupPrefix/subget/{p1}": {
+      "get": {
+        "tags": [
+          "GroupPrefix"
+        ],
+        "operationId": "groupPrefix_subget",
+        "parameters": [
+          {
+            "name": "p1",
+            "in": "path",
+            "required": true,
+            "schema": {
+              "type": "integer",
+              "format": "int32"
+            }
+          },
+          {
+            "name": "X-H1",
+            "in": "header",
+            "required": true,
+            "schema": {
+              "type": "integer",
+              "format": "int32"
+            }
+          },
+          {
+            "name": "q1",
+            "in": "query",
+            "required": true,
+            "explode": false,
+            "schema": {
+              "type": "integer",
+              "format": "int32"
+            }
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "Success",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "type": "string"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/jsonFailingGet": {
       "get": {
         "operationId": "jsonFailingGet",
@@ -956,6 +1006,9 @@
       "name": "Prefix",
       "description": "example API subgroup"
     },
+    {
+      "name": "GroupPrefix"
+    },
     {
       "name": "TrivialGroup"
     },
diff --git a/rest/src/main/scala/io/udash/rest/openapi/OpenApiMetadata.scala b/rest/src/main/scala/io/udash/rest/openapi/OpenApiMetadata.scala
index ef645e03b..a656dedbc 100644
--- a/rest/src/main/scala/io/udash/rest/openapi/OpenApiMetadata.scala
+++ b/rest/src/main/scala/io/udash/rest/openapi/OpenApiMetadata.scala
@@ -54,12 +54,13 @@ final case class OpenApiMetadata[T](
 
   // collect all tags
   private lazy val openApiTags: List[Tag] = {
-    def createTags(method: OpenApiMethod[_]): List[Tag] =
-      method.groupAnnot.fold[List[Tag]](Nil) { group =>
-        List(method.tagAdjusters.foldLeft(Tag(group.groupName))({ case (tag, adjuster) => adjuster.adjustTag(tag) }))
+    def createTag(method: OpenApiMethod[_]): Opt[Tag] =
+      method.groupAnnot.map { group =>
+        method.tagAdjusters.foldLeft(Tag(group.groupName))({ case (tag, adjuster) => adjuster.adjustTag(tag) })
       }
 
-    prefixes.flatMap(prefix => createTags(prefix) ++ prefix.result.value.openApiTags) ++ httpMethods.flatMap(createTags)
+    (prefixes.iterator.flatMap(prefix => createTag(prefix).iterator ++ prefix.result.value.openApiTags.iterator) ++
+      httpMethods.iterator.flatMap(createTag)).toList
   }
 
   def operations(resolver: SchemaResolver): Iterator[PathOperation] =
diff --git a/rest/src/test/scala/io/udash/rest/RestTestApi.scala b/rest/src/test/scala/io/udash/rest/RestTestApi.scala
index 8deaf1b61..492fdab4a 100644
--- a/rest/src/test/scala/io/udash/rest/RestTestApi.scala
+++ b/rest/src/test/scala/io/udash/rest/RestTestApi.scala
@@ -131,6 +131,9 @@ trait RestTestApi {
     @Query @example("q0example") q0: String
   ): RestTestSubApi
 
+  @group
+  def groupPrefix: RestTestSubApi
+
   @Prefix("") def transparentPrefix: RestTestSubApi
 
   def complexParams(
@@ -172,6 +175,7 @@ object RestTestApi extends DefaultRestApiCompanion[RestTestApi] {
       Future.successful(s"$q1-$p1-$p2")
     def prefix(p0: String, h0: String, q0: String): RestTestSubApi =
       RestTestSubApi.impl(s"$p0-$h0-$q0")
+    def groupPrefix: RestTestSubApi = RestTestSubApi.impl("")
     def transparentPrefix: RestTestSubApi = RestTestSubApi.impl("")
     def complexParams(baseEntity: BaseEntity, flatBaseEntity: Opt[FlatBaseEntity]): Future[Unit] = Future.unit
     def complexParams(flatBaseEntity: FlatBaseEntity, baseEntity: Opt[BaseEntity]): Future[Unit] = Future.unit