diff --git a/core/src/main/scala/caliban/execution/Executor.scala b/core/src/main/scala/caliban/execution/Executor.scala
index 6e6992d68..c0a1adb80 100644
--- a/core/src/main/scala/caliban/execution/Executor.scala
+++ b/core/src/main/scala/caliban/execution/Executor.scala
@@ -12,6 +12,8 @@ import caliban.wrappers.Wrapper.FieldWrapper
 import zio._
 import zio.query.ZQuery
 
+import scala.collection.mutable.ArrayBuffer
+
 object Executor {
 
   /**
@@ -51,7 +53,7 @@ object Executor {
           value match {
             case EnumValue(v) =>
               // special case of an hybrid union containing case objects, those should return an object instead of a string
-              val obj = filterFields(currentField, v).collectFirst {
+              val obj = mergeFields(currentField, v).collectFirst {
                 case f: Field if f.name == "__typename" =>
                   ObjectValue(List(f.alias.getOrElse(f.name) -> StringValue(v)))
                 case f: Field if f.name == "_"          =>
@@ -70,7 +72,7 @@ object Executor {
             Types.listOf(currentField.fieldType).fold(false)(_.isNullable)
           )
         case ObjectStep(objectName, fields) =>
-          val filteredFields = filterFields(currentField, objectName)
+          val filteredFields = mergeFields(currentField, objectName)
           val items          = filteredFields.map {
             case f @ Field(name @ "__typename", _, _, alias, _, _, _, _, directives) =>
               (alias.getOrElse(name), PureStep(StringValue(objectName)), fieldInfo(f, path, directives))
@@ -172,8 +174,31 @@ object Executor {
   private[caliban] def fail(error: CalibanError): UIO[GraphQLResponse[CalibanError]] =
     IO.succeed(GraphQLResponse(NullValue, List(error)))
 
-  private[caliban] def filterFields(field: Field, typeName: String): List[Field] =
-    field.fields.filter(_.condition.forall(_.contains(typeName)))
+  private[caliban] def mergeFields(field: Field, typeName: String): List[Field] = {
+    // ugly mutable code but it's worth it for the speed ;)
+    val array = ArrayBuffer.empty[Field]
+    val map   = collection.mutable.Map.empty[String, Int]
+    var index = 0
+
+    field.fields.foreach { field =>
+      if (field.condition.forall(_.contains(typeName))) {
+        val name = field.alias.getOrElse(field.name)
+        map.get(name) match {
+          case None        =>
+            // first time we see this field, add it to the array
+            array += field
+            map.update(name, index)
+            index = index + 1
+          case Some(index) =>
+            // field already existed, merge it
+            val f = array(index)
+            array(index) = f.copy(fields = f.fields ::: field.fields)
+        }
+      }
+    }
+
+    array.toList
+  }
 
   private def fieldInfo(field: Field, path: List[Either[String, Int]], fieldDirectives: List[Directive]): FieldInfo =
     FieldInfo(field.alias.getOrElse(field.name), field, path, fieldDirectives)
diff --git a/core/src/main/scala/caliban/execution/Field.scala b/core/src/main/scala/caliban/execution/Field.scala
index 73b445083..664a7bfd6 100644
--- a/core/src/main/scala/caliban/execution/Field.scala
+++ b/core/src/main/scala/caliban/execution/Field.scala
@@ -37,16 +37,17 @@ object Field {
   ): Field = {
     def loop(selectionSet: List[Selection], fieldType: __Type): Field = {
       val fieldList  = ArrayBuffer.empty[Field]
-      val map        = collection.mutable.Map.empty[String, Int]
+      val map        = collection.mutable.Map.empty[(String, String), Int]
       var fieldIndex = 0
 
-      def addField(f: Field): Unit = {
+      def addField(f: Field, condition: Option[String]): Unit = {
         val name = f.alias.getOrElse(f.name)
-        map.get(name) match {
+        val key  = (name, condition.getOrElse(""))
+        map.get(key) match {
           case None        =>
             // first time we see this field, add it to the array
             fieldList += f
-            map.update(name, fieldIndex)
+            map.update(key, fieldIndex)
             fieldIndex = fieldIndex + 1
           case Some(index) =>
             // field already existed, merge it
@@ -88,7 +89,8 @@ object Field {
               resolveVariables(arguments, variableDefinitions, variableValues),
               () => sourceMapper.getLocation(index),
               directives ++ schemaDirectives
-            )
+            ),
+            None
           )
         case FragmentSpread(name, directives) if checkDirectives(directives, variableValues)                        =>
           fragments
@@ -101,7 +103,7 @@ object Field {
                   if (field.condition.isDefined) field
                   else field.copy(condition = subtypeNames(f.typeCondition.name, rootType))
                 )
-                .foreach(addField)
+                .foreach(addField(_, Some(f.typeCondition.name)))
             }
         case InlineFragment(typeCondition, directives, selectionSet) if checkDirectives(directives, variableValues) =>
           val t     = innerType.possibleTypes
@@ -116,7 +118,7 @@ object Field {
                   if (field.condition.isDefined) field
                   else field.copy(condition = subtypeNames(typeName.name, rootType))
                 )
-                .foreach(addField)
+                .foreach(addField(_, Some(typeName.name)))
           }
         case _                                                                                                      =>
       }
diff --git a/core/src/test/scala/caliban/execution/ExecutionSpec.scala b/core/src/test/scala/caliban/execution/ExecutionSpec.scala
index 6f531e865..04b0c8e92 100644
--- a/core/src/test/scala/caliban/execution/ExecutionSpec.scala
+++ b/core/src/test/scala/caliban/execution/ExecutionSpec.scala
@@ -20,6 +20,35 @@ import zio.test.environment.TestEnvironment
 
 object ExecutionSpec extends DefaultRunnableSpec {
 
+  @GQLInterface
+  sealed trait Base {
+    def id: String
+    def name: String
+  }
+  object Base {
+    @GQLName("BaseOne")
+    case class One(
+      id: String,
+      name: String,
+      inner: List[One.Inner]
+    ) extends Base
+    object One {
+      @GQLName("BaseOneInner")
+      case class Inner(a: String)
+    }
+
+    @GQLName("BaseTwoOne")
+    case class Two(
+      id: String,
+      name: String,
+      inner: List[Two.Inner]
+    ) extends Base
+    object Two {
+      @GQLName("BaseTwoInner")
+      case class Inner(b: Int)
+    }
+  }
+
   override def spec: ZSpec[TestEnvironment, Any] =
     suite("ExecutionSpec")(
       testM("skip directive") {
@@ -1128,6 +1157,47 @@ object ExecutionSpec extends DefaultRunnableSpec {
             """{"test":2}"""
           )
         )
+      },
+      testM("conflicting fragments selection merging") {
+
+        val base1 = Base.One(
+          id = "1",
+          name = "base 1",
+          inner = List(Base.One.Inner(a = "a"))
+        )
+        val base2 = Base.Two(
+          id = "2",
+          name = "base 2",
+          inner = List(Base.Two.Inner(b = 2))
+        )
+        case class Test(bases: List[Base])
+
+        implicit val baseSchema: Schema[Any, Base] = Schema.gen
+
+        val api   = graphQL(RootResolver(Test(List(base1, base2))))
+        val query = """
+        query {
+          bases {
+            id
+            ... on BaseOne {
+              id
+              name
+              inner { a }
+            }
+            ... on BaseTwoOne {
+              id
+              name
+              inner { b }
+            }
+          }
+        }
+      """
+
+        api.interpreter.flatMap(_.execute(query)).map { response =>
+          assertTrue(
+            response.data.toString == """{"bases":[{"id":"1","name":"base 1","inner":[{"a":"a"}]},{"id":"2","name":"base 2","inner":[{"b":2}]}]}"""
+          )
+        }
       }
     )
 }