diff --git a/tox_poetry_installer/hooks.py b/tox_poetry_installer/hooks.py
index 1cd0e76..984c6a7 100644
--- a/tox_poetry_installer/hooks.py
+++ b/tox_poetry_installer/hooks.py
@@ -112,7 +112,9 @@ def tox_testenv_install_deps(venv: ToxVirtualEnv, action: ToxAction) -> Optional
 
         env_deps: List[PoetryPackage] = []
         for dep in venv.envconfig.locked_deps:
-            env_deps += utilities.find_transients(package_map, dep.lower())
+            env_deps += utilities.find_transients(
+                package_map, dep.lower(), allow_missing=[poetry.package.name]
+            )
         reporter.verbosity1(
             f"{constants.REPORTER_PREFIX} Identified {len(env_deps)} environment dependencies to install to env"
         )
diff --git a/tox_poetry_installer/utilities.py b/tox_poetry_installer/utilities.py
index d2d84c9..8aee0c1 100644
--- a/tox_poetry_installer/utilities.py
+++ b/tox_poetry_installer/utilities.py
@@ -48,13 +48,17 @@ def install_to_venv(
         installer.install(dependency)
 
 
-def find_transients(packages: PackageMap, dependency_name: str) -> Set[PoetryPackage]:
+def find_transients(
+    packages: PackageMap, dependency_name: str, allow_missing: Sequence[str] = ()
+) -> Set[PoetryPackage]:
     """Using a poetry object identify all dependencies of a specific dependency
 
-    :param poetry: Populated poetry object which can be used to build a populated locked
-                   repository object.
+    :param packages: All packages from the lockfile to use for identifying dependency relationships.
     :param dependency_name: Bare name (without version) of the dependency to fetch the transient
                             dependencies of.
+    :param allow_missing: Sequence of package names to allow to be missing from the lockfile. Any
+                          packages that are not found in the lockfile but their name appears in this
+                          list will be silently skipped from installation.
     :returns: List of packages that need to be installed for the requested dependency.
 
     .. note:: The package corresponding to the dependency named by ``dependency_name`` is included
@@ -75,7 +79,15 @@ def find_transients(packages: PackageMap, dependency_name: str) -> Set[PoetryPac
             return dict()
 
         transients: PackageMap = {}
-        package = packages[name]
+        try:
+            package = packages[name]
+        except KeyError as err:
+            if name in allow_missing:
+                reporter.verbosity2(
+                    f"{constants.REPORTER_PREFIX} Skip {name}: package is not in lockfile but designated as allowed to be missing"
+                )
+                return dict()
+            raise err
 
         if not package.python_constraint.allows(constants.PLATFORM_VERSION):
             reporter.verbosity2(
@@ -190,6 +202,8 @@ def find_project_dependencies(
 
     dependencies: List[PoetryPackage] = []
     for dep in base_dependencies + extra_dependencies:
-        dependencies += find_transients(packages, dep.name.lower())
+        dependencies += find_transients(
+            packages, dep.name.lower(), allow_missing=[poetry.package.name]
+        )
 
     return dependencies