diff --git a/src/poetry/packages/locker.py b/src/poetry/packages/locker.py
index 44a88ca3a17..b17a6d7e404 100644
--- a/src/poetry/packages/locker.py
+++ b/src/poetry/packages/locker.py
@@ -36,9 +36,9 @@
 
 
 if TYPE_CHECKING:
+    from poetry.core.version.markers import BaseMarker
     from tomlkit.toml_document import TOMLDocument
 
-    from poetry.core.version.markers import BaseMarker
     from poetry.repositories import Repository
 
 logger = logging.getLogger(__name__)
@@ -240,6 +240,7 @@ def __walk_dependencies(
         cls,
         dependencies: List[Dependency],
         packages_by_name: Dict[str, List[Package]],
+        extras: Union[bool, Sequence[str]] = False,
     ) -> Dict[Package, Dependency]:
         nested_dependencies: Dict[Package, Dependency] = {}
 
@@ -255,10 +256,7 @@ def __walk_dependencies(
             )
 
             if not locked_package:
-                # Should normally be able to satisfy all requirements, but this case is
-                # permissible eg if we encounter a dev dependency when walking the
-                # non-dev dependencies.
-                continue
+                raise RuntimeError(f"Dependency walk failed at {requirement}")
 
             # create dependency from locked package to retain dependency metadata
             # if this is not done, we can end-up with incorrect nested dependencies
@@ -270,6 +268,16 @@ def __walk_dependencies(
             requirement.set_constraint(constraint)
 
             for require in locked_package.requires:
+                # Ignore unwanted extras.
+                if require.is_optional():
+                    keep = (
+                        extras
+                        if isinstance(extras, bool)
+                        else any(extra in require.in_extras for extra in extras)
+                    )
+                    if not keep:
+                        continue
+
                 require = deepcopy(require)
                 require.marker = require.marker.intersect(requirement.marker)
                 if not require.marker.is_empty():
@@ -290,7 +298,9 @@ def get_project_dependencies(
         cls,
         project_requires: List[Dependency],
         locked_packages: List[Package],
+        extras: Optional[Union[bool, Sequence[str]]] = None,
     ) -> Iterable[Tuple[Package, Dependency]]:
+        extras = extras or False
         # group packages entries by name, this is required because requirement might use
         # different constraints.
         packages_by_name = {}
@@ -323,6 +333,7 @@ def get_project_dependencies(
         nested_dependencies = cls.__walk_dependencies(
             dependencies=dependencies,
             packages_by_name=packages_by_name,
+            extras=extras,
         )
 
         return nested_dependencies.items()
@@ -368,6 +379,7 @@ def get_project_dependency_packages(
         for package, dependency in self.get_project_dependencies(
             project_requires=selected,
             locked_packages=repository.packages,
+            extras=extras,
         ):
             for extra in dependency.extras:
                 package.requires_extras.append(extra)