diff --git a/tox_poetry_installer/exceptions.py b/tox_poetry_installer/exceptions.py
index 44d476f..b789e19 100644
--- a/tox_poetry_installer/exceptions.py
+++ b/tox_poetry_installer/exceptions.py
@@ -11,6 +11,7 @@ All exceptions should inherit from the common base exception :exc:`ToxPoetryInst
    +-- LockedDepNotFoundError
    +-- ExtraNotFoundError
    +-- LockedDepsRequiredError
+   +-- RequiresUnsafeDepError
 
 """
 
@@ -41,3 +42,7 @@ class ExtraNotFoundError(ToxPoetryInstallerException):
 
 class LockedDepsRequiredError(ToxPoetryInstallerException):
     """Environment cannot specify unlocked dependencies when locked dependencies are required"""
+
+
+class RequiresUnsafeDepError(ToxPoetryInstallerException):
+    """Package under test depends on an unsafe dependency and cannot be installed"""
diff --git a/tox_poetry_installer/utilities.py b/tox_poetry_installer/utilities.py
index 87e1d98..ee12501 100644
--- a/tox_poetry_installer/utilities.py
+++ b/tox_poetry_installer/utilities.py
@@ -166,6 +166,11 @@ def find_project_deps(
     :param extras: Sequence of extra names to include the dependencies of
     """
 
+    if any(dep.name in constants.UNSAFE_PACKAGES for dep in poetry.package.requires):
+        raise exceptions.RequiresUnsafeDepError(
+            f"Project package requires one or more unsafe dependencies ({', '.join(constants.UNSAFE_PACKAGES)}) which cannot be installed with Poetry"
+        )
+
     base_deps: List[PoetryPackage] = [
         packages[item.name]
         for item in poetry.package.requires