diff --git a/README.rst b/README.rst
index dfb1ed92c..d0a664588 100644
--- a/README.rst
+++ b/README.rst
@@ -130,6 +130,10 @@ Now compile and install sire:
 
 A small word of warning, the compilation can easily take over an hour!
 
+If `ccache <https://ccache.dev>`__ is on your ``PATH``, then ``setup.py`` will
+use it automatically, which makes rebuilds much faster when developing. It
+isn't included in the pixi environments, so install it separately if needed.
+
 Other pixi environments are available depending on your needs:
 
 * ``pixi install -e default`` - core sire dependencies only
diff --git a/corelib/src/libs/SireVol/triclinicbox.cpp b/corelib/src/libs/SireVol/triclinicbox.cpp
index 9f6ddad85..98e133cd6 100644
--- a/corelib/src/libs/SireVol/triclinicbox.cpp
+++ b/corelib/src/libs/SireVol/triclinicbox.cpp
@@ -74,6 +74,9 @@ QDataStream &operator>>(QDataStream &ds, TriclinicBox &box)
     else if (v == 2)
     {
         ds >> box.v0 >> box.v1 >> box.v2 >> box.rotation_matrix >> box.cell_matrix >> box.cell_matrix_inverse >> box.dist_max >> box._alpha >> box._beta >> box._gamma >> box.vol >> box.is_rotated >> box.is_reduced >> box.invlength;
+
+        // M and max_length aren't streamed, so recompute them.
+        box.setAttributes();
     }
     else
         throw version_error(v, "1,2", r_box, CODELOC);
@@ -269,7 +272,6 @@ void TriclinicBox::rotate(double precision)
         this->v1.setZ(0);
     }
 
-
     // Now set the box attributes.
     this->setAttributes();
 }
@@ -405,6 +407,7 @@ TriclinicBox &TriclinicBox::operator=(const TriclinicBox &other)
         rotation_matrix = other.rotation_matrix;
         cell_matrix = other.cell_matrix;
         cell_matrix_inverse = other.cell_matrix_inverse;
+        M = other.M;
         dist_max = other.dist_max;
         max_length = other.max_length;
         _alpha = other._alpha;
@@ -571,7 +574,7 @@ SireUnits::Dimension::Length TriclinicBox::maximumCutoff() const
     if (this->isReduced())
     {
         QList<double> diagonals = {this->v0.x(), this->v1.y(), this->v2.z()};
-        return SireUnits::Dimension::Length(*std::min_element(diagonals.begin(), diagonals.end())/2.0);
+        return SireUnits::Dimension::Length(*std::min_element(diagonals.begin(), diagonals.end()) / 2.0);
     }
     // Otherwise, use half the norm of the smallest box vector.
     else
diff --git a/doc/source/changelog.rst b/doc/source/changelog.rst
index 2ac03be4c..4bcf91be9 100644
--- a/doc/source/changelog.rst
+++ b/doc/source/changelog.rst
@@ -58,6 +58,10 @@ organisation on `GitHub <https://github.com/openbiosim/sire>`__.
   bindings. Structures are now exchanged with the gemmi Python module using gemmi's
   own binary serialization, removing the pybind11 dependency.
 
+* Fixed ``TriclinicBox`` losing its metric matrix when streamed or assigned, which gave
+  wrong minimum image distances from ``calc_dist``, e.g. for trajectory frame spaces. This
+  broke ``sire.restraints.boresch_search()`` for triclinic boxes.
+
 `2026.2.0 <https://github.com/openbiosim/sire/compare/2026.1.0...2026.2.0>`__ - September 2026
 ----------------------------------------------------------------------------------------------
 
diff --git a/tests/vol/test_triclinic.py b/tests/vol/test_triclinic.py
index c9e929ea5..8112a899b 100644
--- a/tests/vol/test_triclinic.py
+++ b/tests/vol/test_triclinic.py
@@ -143,6 +143,43 @@ def test_stream():
     assert recovered_box == box
 
 
+def test_stream_calc_dist():
+    """
+    Test that a streamed TriclinicBox gives the same minimum image distance
+    as the original.
+    """
+
+    tmp_dir = tempfile.TemporaryDirectory()
+    s3_file = f"{tmp_dir.name}/box.s3"
+
+    box = sr.vol.TriclinicBox.truncated_octahedron(50.0, True, True)
+
+    sr.stream.save(box, s3_file)
+    recovered_box = sr.stream.load(s3_file)
+
+    p0 = sr.maths.Vector(1, 2, 3)
+    p1 = sr.maths.Vector(7, -2, 5)
+    dist = sr.maths.Vector.distance(p0, p1).value()
+
+    assert box.calc_dist(p0, p1) == pytest.approx(dist)
+    assert recovered_box.calc_dist(p0, p1) == pytest.approx(dist)
+
+
+def test_default_calc_dist():
+    """
+    Test that a default constructed TriclinicBox gives Cartesian distances.
+    """
+
+    box = sr.vol.TriclinicBox()
+
+    p0 = sr.maths.Vector(1, 2, 3)
+    p1 = sr.maths.Vector(7, -2, 5)
+
+    assert box.calc_dist(p0, p1) == pytest.approx(
+        sr.maths.Vector.distance(p0, p1).value()
+    )
+
+
 def test_max_cutoff(ala_mols):
     """
     Test that the maximum cutoff is set correctly.