diff --git a/mesonbuild/build.py b/mesonbuild/build.py
index 06e40f571..a4a4f1916 100644
--- a/mesonbuild/build.py
+++ b/mesonbuild/build.py
@@ -40,7 +40,7 @@ from .linkers import StaticLinker
 from .interpreterbase import FeatureNew
 
 if T.TYPE_CHECKING:
-    from .interpreter import Test
+    from .interpreter.interpreter import Test, SourceOutputs
     from .mesonlib import FileMode, FileOrString
     from .mesonlib.backend import Backend
 
@@ -589,12 +589,11 @@ class BuildTarget(Target):
     known_kwargs = known_build_target_kwargs
 
     def __init__(self, name: str, subdir: str, subproject: str, for_machine: MachineChoice,
-                 sources: T.List[File], objects, environment: environment.Environment, kwargs):
+                 sources: T.List['SourceOutputs'], objects, environment: environment.Environment, kwargs):
         super().__init__(name, subdir, subproject, True, for_machine)
         unity_opt = environment.coredata.get_option(OptionKey('unity'))
         self.is_unity = unity_opt == 'on' or (unity_opt == 'subprojects' and subproject != '')
         self.environment = environment
-        self.sources: T.List[File] = []
         self.compilers = OrderedDict() # type: OrderedDict[str, Compiler]
         self.objects = []
         self.external_deps = []
@@ -613,6 +612,7 @@ class BuildTarget(Target):
         self.need_install = False
         self.pch = {}
         self.extra_args: T.Dict[str, T.List['FileOrString']] = {}
+        self.sources: T.List[File] = []
         self.generated: T.Sequence[T.Union[GeneratedList, CustomTarget, CustomTargetIndex]] = []
         self.d_features = {}
         self.pic = False
diff --git a/mesonbuild/interpreter/interpreter.py b/mesonbuild/interpreter/interpreter.py
index 891f67eff..484db7866 100644
--- a/mesonbuild/interpreter/interpreter.py
+++ b/mesonbuild/interpreter/interpreter.py
@@ -68,8 +68,9 @@ if T.TYPE_CHECKING:
     SourceInputs = T.Union[mesonlib.File, GeneratedListHolder, TargetHolder,
                            CustomTargetIndexHolder, GeneratedObjectsHolder, str]
     # Input source types passed to the build.Target5 classes
-    SourceOutputs = T.Union[mesonlib.File, GeneratedListHolder, TargetHolder,
-                            CustomTargetIndexHolder, GeneratedObjectsHolder]
+    SourceOutputs = T.Union[mesonlib.File, build.GeneratedList,
+                            build.BuildTarget, build.CustomTargetIndex,
+                            build.GeneratedList]
 
 def stringifyUserArguments(args, quote=False):
     if isinstance(args, list):
@@ -2705,13 +2706,16 @@ Try setting b_lundef to false instead.'''.format(self.coredata.options[OptionKey
         for s in sources:
             if isinstance(s, str):
                 self.validate_within_subproject(self.subdir, s)
-                s = mesonlib.File.from_source_file(self.environment.source_dir, self.subdir, s)
-            elif not isinstance(s, (mesonlib.File, GeneratedListHolder,
-                                    TargetHolder, CustomTargetIndexHolder,
-                                    GeneratedObjectsHolder)):
-                raise InterpreterException('Source item is {!r} instead of '
-                                           'string or File-type object'.format(s))
-            results.append(s)
+                results.append(mesonlib.File.from_source_file(self.environment.source_dir, self.subdir, s))
+            elif isinstance(s, mesonlib.File):
+                results.append(s)
+            elif isinstance(s, (GeneratedListHolder, TargetHolder,
+                                CustomTargetIndexHolder,
+                                GeneratedObjectsHolder)):
+                results.append(unholder(s))
+            else:
+                raise InterpreterException(f'Source item is {s!r} instead of '
+                                           'string or File-type object')
         return results
 
     def add_target(self, name, tobj):