diff --git a/loopy/symbolic.py b/loopy/symbolic.py
index 60473ada580fdca7b618f8e33086e0d7ea9f267a..f5cf07b0e1d62212ce36edb48f47eb7de7d31451 100644
--- a/loopy/symbolic.py
+++ b/loopy/symbolic.py
@@ -866,7 +866,8 @@ class RuleAwareIdentityMapper(IdentityMapper):
         if name not in self.rule_mapping_context.old_subst_rules:
             return super(RuleAwareIdentityMapper, self).map_call(expr, expn_state)
         else:
-            return self.map_substitution(name, tag, expr.parameters, expn_state)
+            return self.map_substitution(name, tag, self.rec(
+                expr.parameters, expn_state), expn_state)
 
     @staticmethod
     def make_new_arg_context(rule_name, arg_names, arguments, arg_context):
diff --git a/loopy/transform/subst.py b/loopy/transform/subst.py
index a681afe06520483c83530c241e39229412e88f03..b92698ffa1e84455be3f79bed7dbf884f36be490 100644
--- a/loopy/transform/subst.py
+++ b/loopy/transform/subst.py
@@ -469,6 +469,13 @@ def assignment_to_subst(kernel, lhs_name, extra_arguments=(), within=None,
 # {{{ expand_subst
 
 def expand_subst(kernel, within=None):
+    """
+    Returns an instance of :class:`loopy.LoopKernel` with the substitutions
+    referenced in instructions of *kernel* matched by *within* expanded.
+
+    :arg within: a stack match as understood by
+        :func:`loopy.match.parse_stack_match`.
+    """
     if not kernel.substitutions:
         return kernel
 
diff --git a/test/test_transform.py b/test/test_transform.py
index 394cf668804ed719920e02bc3d20f62971421c2f..3ee67b703964d1f7773b10a9199687d78b883a60 100644
--- a/test/test_transform.py
+++ b/test/test_transform.py
@@ -550,6 +550,26 @@ def test_split_iname_only_if_in_within():
             assert insn.within_inames == frozenset({'i'})
 
 
+def test_nested_substs_in_insns(ctx_factory):
+    ctx = ctx_factory()
+    import loopy as lp
+
+    ref_knl = lp.make_kernel(
+        "{[i]: 0<=i<10}",
+        """
+        a(x) := 2 * x
+        b(x) := x**2
+        c(x) := 7 * x
+        f[i] = c(b(a(i)))
+        """
+    )
+
+    knl = lp.expand_subst(ref_knl)
+    assert not knl.substitutions
+
+    lp.auto_test_vs_ref(ref_knl, ctx, knl)
+
+
 if __name__ == "__main__":
     if len(sys.argv) > 1:
         exec(sys.argv[1])