diff --git a/glassure/core/pattern.py b/glassure/core/pattern.py
index 2ae61a8..bdc93f7 100644
--- a/glassure/core/pattern.py
+++ b/glassure/core/pattern.py
@@ -331,7 +331,7 @@ def __sub__(self, other: Pattern) -> Pattern:
         if orig_x.shape != other_x.shape:
             # todo different shape subtraction of spectra seems the fail somehow...
             # the background will be interpolated
-            other_fcn = interp1d(other_x, other_x, kind='linear')
+            other_fcn = interp1d(other_x, other_y, kind='linear')
 
             # find overlapping x and y values:
             ind = np.where((orig_x <= np.max(other_x)) &
@@ -362,7 +362,7 @@ def __add__(self, other: Pattern) -> Pattern:
 
         if orig_x.shape != other_x.shape:
             # the background will be interpolated
-            other_fcn = interp1d(other_x, other_x, kind='linear')
+            other_fcn = interp1d(other_x, other_y, kind='linear')
 
             # find overlapping x and y values:
             ind = np.where((orig_x <= np.max(other_x)) &
diff --git a/tests/core_tests/test_pattern.py b/tests/core_tests/test_pattern.py
index 05a709e..9481ac5 100644
--- a/tests/core_tests/test_pattern.py
+++ b/tests/core_tests/test_pattern.py
@@ -31,6 +31,20 @@ def test_plus_and_minus_operators():
     assert np.array_equal(pattern1._y, np.sin(x) * 1)
 
 
+def test_plus_and_minus_operators_with_different_x():
+    x1 = np.linspace(1, 9, 1000)
+    x2 = np.linspace(0, 10, 998)
+    pattern1 = Pattern(x1, np.sin(x1))
+    pattern2 = Pattern(x2, np.sin(x2))
+
+    pattern3 = pattern1 + pattern2
+    assert np.array_equal(pattern3.x, x1)
+    np.testing.assert_array_almost_equal(pattern3.y, np.sin(x1) * 2, decimal=5)
+
+    pattern3 = pattern1 - pattern2
+    np.testing.assert_array_almost_equal(pattern3._y, np.sin(x1) * 0, decimal=5)
+
+
 def test_multiply_operator():
     x = np.linspace(0, 10, 100)
     pattern = 2 * Pattern(x, np.sin(x))