diff --git a/CADETProcess/comparison/comparator.py b/CADETProcess/comparison/comparator.py
index 4c0a8752f..bef01c989 100644
--- a/CADETProcess/comparison/comparator.py
+++ b/CADETProcess/comparison/comparator.py
@@ -1,6 +1,7 @@
 import copy
 import importlib
 import functools
+import warnings
 
 import numpy as np
 import matplotlib.pyplot as plt
@@ -121,20 +122,19 @@ def labels(self):
 
         return labels
 
-    @functools.wraps(DifferenceBase.__init__)
     def add_difference_metric(
-            self, difference_metric, reference, solution_path,
+            self, difference_metric, solution_path, reference,
             *args, **kwargs):
         """Add a difference metric to the Comparator.
 
         Parameters
         ----------
-        difference_metric : str
-            Name of the difference metric to be evaluated.
-        reference : str or SolutionBase
-            Name of the reference or reference itself.
+        difference_metric : DifferenceMetricBase
+            Difference metric to be evaluated.
         solution_path : str
             Path to the solution in SimulationResults.
+        reference : str or SolutionBase
+            Name of the reference or reference itself.
         *args, **kwargs
             Additional arguments and keyword arguments to be passed to the
             difference metric constructor.
@@ -144,29 +144,36 @@ def add_difference_metric(
         CADETProcessError
             If the difference metric or reference is unknown.
         """
-        try:
-            module = importlib.import_module(
-                'CADETProcess.comparison.difference'
+        if isinstance(difference_metric, str):
+            warnings.warn(
+                'This method of adding difference metrics is deprecated. '
+                'Instead, pass an instance of the desired metric class.',
+                DeprecationWarning, stacklevel=2
             )
-            cls_ = getattr(module, difference_metric)
-        except KeyError:
-            raise CADETProcessError("Unknown Metric Type.")
+            if isinstance(reference, SolutionBase):
+                reference = reference.name
 
-        if isinstance(reference, SolutionBase):
-            reference = reference.name
+            if reference not in self.references:
+                raise CADETProcessError("Unknown Reference.")
 
-        if reference not in self.references:
-            raise CADETProcessError("Unknown Reference.")
-
-        reference = self.references[reference]
-
-        metric = cls_(reference, *args, **kwargs)
+            reference = self.references[reference]
+            try:
+                module = importlib.import_module(
+                    'CADETProcess.comparison.difference'
+                )
+                cls_ = getattr(module, difference_metric)
+                difference_metric = cls_(reference, *args, **kwargs)
+            except KeyError:
+                raise CADETProcessError("Unknown Difference Metric.")
+        else:
+            if not isinstance(difference_metric, DifferenceBase):
+                raise TypeError("Expected DifferenceBase.")
 
-        self.solution_paths[metric] = solution_path
+        self.solution_paths[difference_metric] = solution_path
 
-        self._metrics.append(metric)
+        self._metrics.append(difference_metric)
 
-        return metric
+        return difference_metric
 
     def extract_solution(self, simulation_results, metric):
         """Extract the solution for a given metric from the SimulationResults object.