diff --git a/devito/ir/equations/algorithms.py b/devito/ir/equations/algorithms.py
index e0281e1139..7717fb79eb 100644
--- a/devito/ir/equations/algorithms.py
+++ b/devito/ir/equations/algorithms.py
@@ -254,7 +254,7 @@ def _(d, mapper, rebuilt, sregistry):
 
         if any(v in mapper for v in d.condition.free_symbols):
             # Substitute into condition
-            kwargs['condition'] = d.condition.subs(mapper)
+            kwargs['condition'] = d.condition.xreplace(mapper)
 
     if kwargs:
         # Rebuild if parent or condition need replacing
diff --git a/tests/test_dimension.py b/tests/test_dimension.py
index 84df27ecef..da2d98252a 100644
--- a/tests/test_dimension.py
+++ b/tests/test_dimension.py
@@ -16,7 +16,7 @@
 from devito.ir import SymbolRegistry
 from devito.symbolics import indexify, retrieve_functions, IntDiv, INT
 from devito.types import Array, StencilDimension, Symbol
-from devito.types.dimension import AffineIndexAccessFunction
+from devito.types.dimension import AffineIndexAccessFunction, Thickness
 
 
 class TestIndexAccessFunction:
@@ -2055,3 +2055,39 @@ def test_correct_thicknesses(self):
         assert rebuilt[0].is_left
         assert rebuilt[1].is_right
         assert rebuilt[2].is_middle
+
+    def test_condition_concretization(self):
+        """
+        Check thicknesses in conditionals get concretized correctly, including in
+        cases where there are multiple such conditions.
+        """
+        x = Dimension('x')
+
+        ix0 = SubDimension.left('ix', x, 6)
+        ix1 = SubDimension.middle('ix', x, 2, 1)
+
+        cond0 = Gt(x, ix0.ltkn)
+        cond1 = Gt(x, ix1.ltkn)
+
+        cdim0 = ConditionalDimension('cdim0', parent=x, condition=cond0)
+        cdim1 = ConditionalDimension('cdim1', parent=x, condition=cond1)
+
+        f = Function(name='f', dimensions=(x,), shape=(11,))
+
+        eqs = [Eq(f, 1, implicit_dims=cdim0), Eq(f, 1, implicit_dims=cdim1)]
+
+        op = Operator(eqs)
+
+        # Check correct conditionals are in the generated code
+        assert "if (x > x_ltkn0)" in str(op.ccode)
+        assert "if (x > x_ltkn1)" in str(op.ccode)
+
+        expected_conditionals = [Gt(x, p) for p in op.parameters
+                                 if isinstance(p, Thickness)]
+
+        conditionals = FindNodes(Conditional).visit(op)
+        assert len(conditionals) == 2
+        # Check that the two conditions are concretized uniquely
+        assert len({c.condition for c in conditionals}) == 2
+        for c in conditionals:
+            assert c.condition in expected_conditionals