diff --git a/tests/test_model_breit_wigner.py b/tests/test_model_breit_wigner.py
index 3d3c99f..10af9d4 100644
--- a/tests/test_model_breit_wigner.py
+++ b/tests/test_model_breit_wigner.py
@@ -1,6 +1,7 @@
 """Example test for a pdf or function"""
-
+import pytest
 import zfit
+import numpy as np
 # Important, do the imports below
 from zfit.core.testing import setup_function, teardown_function, tester
 
@@ -9,11 +10,23 @@
 # specify globals here. Do NOT add any TensorFlow but just pure python
 param1_true = 0.3
 param2_true = 1.2
+obs1 = zfit.Space("obs1", limits=(-4, 5))
 
 
-def test_special_property1():
+def test_bw_pdf():
     # test special properties  here
-    assert True
+    bw = zphys.unstable.pdf.RelativisticBreitWignerSquared(obs=obs1, mres=1., wres=0.3)
+
+    integral = bw.integrate(limits=obs1)
+    assert pytest.approx(1., rel=1e-3) == zfit.run(integral)
+
+
+def test_bw_func():
+    # test special properties  here
+    bw = zphys.unstable.func.RelativisticBreitWigner(obs=obs1, mres=1., wres=0.3)
+
+    vals = bw.func(x=np.random.uniform(size=(100, 1)))
+    assert 100 == len(zfit.run(vals))
 
 
 # register the pdf here and provide sets of working parameter configurations
@@ -23,5 +36,4 @@ def _bw_params_factory():
     wres = zfit.Parameter('wres', param2_true)
     return {"mres": mres, "wres": wres}
 
-
 # tester.register_func(func_class=zfit.pdf.Gauss, params_factories=_bw_params_factory())
diff --git a/zfit_physics/models/model_breit_wigner.py b/zfit_physics/models/model_breit_wigner.py
index dcac069..73ff21e 100644
--- a/zfit_physics/models/model_breit_wigner.py
+++ b/zfit_physics/models/model_breit_wigner.py
@@ -14,6 +14,32 @@ def relativistic_breit_wigner(m2, mres, wres):
     return 1. / below_div
 
 
+def _bw_func(self, x):
+    """The Breit Wigner function wrapped to be used within a PDF or a Func directly.
+
+    Args:
+        self:
+        x:
+
+    Returns:
+
+    """
+    var = x.unstack_x()
+    if isinstance(var, list):
+        m_sq = kinematics.mass_squared(tf.reduce_sum(
+            [kinematics.lorentz_vector(kinematics.vector(px, py, pz), pe)
+             for px, py, pz, pe in zip(*[iter(var)] * 4)],
+            axis=0))
+    elif self.using_m_squared:
+        m_sq = var
+    else:
+        m_sq = var * tf.math.conj(
+            var)  # TODO(Albert): this was squared, but should be mult with conj, right?
+    mres = self.params['mres']
+    wres = self.params['wres']
+    return relativistic_breit_wigner(m_sq, mres, wres)
+
+
 class RelativisticBreitWigner(zfit.func.BaseFunc):
 
     def __init__(self, obs: ztyping.ObsTypeInput, mres: ztyping.ParamTypeInput, wres: ztyping.ParamTypeInput,
@@ -41,29 +67,20 @@ def __init__(self, obs: ztyping.ObsTypeInput, mres: ztyping.ParamTypeInput, wres
         # HACK end
 
     def _func(self, x):
-        var = x.unstack_x()
-        if isinstance(var, list):
-            m_sq = kinematics.mass_squared(tf.reduce_sum(
-                [kinematics.lorentz_vector(kinematics.vector(px, py, pz), pe)
-                 for px, py, pz, pe in zip(*[iter(var)] * 4)],
-                axis=0))
-        elif self.using_m_squared:
-            m_sq = var
-        else:
-            m_sq = var * tf.math.conj(var)  # TODO(Albert): this was squared, but should be mult with conj, right?
-        mres = self.params['mres']
-        wres = self.params['wres']
-        return relativistic_breit_wigner(m_sq, mres, wres)
-
-
-class RelativisticBreitWignerSquared(RelativisticBreitWigner):
+        return _bw_func(self, x)
+
+
+class RelativisticBreitWignerSquared(zfit.pdf.BasePDF):
 
     def __init__(self, obs: ztyping.ObsTypeInput, mres: ztyping.ParamTypeInput, wres: ztyping.ParamTypeInput,
                  using_m_squared: bool = False, name="RelativisticBreitWignerPDF"):
-        super().__init__(obs=obs, mres=mres, wres=wres, using_m_squared=using_m_squared, name=name)
+        self.using_m_squared = using_m_squared
 
-    def _func(self, x):
-        propagator = super()._func(x)
+        super().__init__(obs=obs, name=name, dtype=zfit.settings.ztypes.float,
+                         params={'mres': mres, 'wres': wres})
+
+    def _unnormalized_pdf(self, x):
+        propagator = _bw_func(self, x)
         val = propagator * tf.math.conj(propagator)
         val = ztf.to_real(val)
         return val
diff --git a/zfit_physics/unstable/__init__.py b/zfit_physics/unstable/__init__.py
index 03949e0..6e7d292 100644
--- a/zfit_physics/unstable/__init__.py
+++ b/zfit_physics/unstable/__init__.py
@@ -1 +1 @@
-from . import pdf
\ No newline at end of file
+from . import pdf, func
\ No newline at end of file
diff --git a/zfit_physics/unstable/func.py b/zfit_physics/unstable/func.py
new file mode 100644
index 0000000..0a7c63f
--- /dev/null
+++ b/zfit_physics/unstable/func.py
@@ -0,0 +1 @@
+from ..models.model_breit_wigner import RelativisticBreitWigner
diff --git a/zfit_physics/unstable/pdf.py b/zfit_physics/unstable/pdf.py
index b19808c..80dd6f3 100644
--- a/zfit_physics/unstable/pdf.py
+++ b/zfit_physics/unstable/pdf.py
@@ -1,2 +1,3 @@
 from ..models.pdf_conv import ConvPDF
-from ..models.pdf_kde import GaussianKDE
\ No newline at end of file
+from ..models.pdf_kde import GaussianKDE
+from ..models.model_breit_wigner import RelativisticBreitWignerSquared
\ No newline at end of file