diff --git a/gusto/equations.py b/gusto/equations.py
index bd61e795b..a1421d0ea 100644
--- a/gusto/equations.py
+++ b/gusto/equations.py
@@ -645,7 +645,7 @@ def __init__(self, domain, parameters, fexpr=None, bexpr=None,
             # Default linearisation is time derivatives, pressure gradient and
             # transport term from depth equation. Don't include active tracers
             linearisation_map = lambda t: \
-                t.get(prognostic) in ['u', 'D'] \
+                t.get(prognostic) in ['u', 'D', 'b'] \
                 and (any(t.has_label(time_derivative, pressure_gradient))
                      or (t.get(prognostic) in ['D', 'b'] and t.has_label(transport)))
         super().__init__(field_names, domain, space_names,