diff --git a/compiler/src/dmd/expressionsem.d b/compiler/src/dmd/expressionsem.d
index f18f61bde222..855809730237 100644
--- a/compiler/src/dmd/expressionsem.d
+++ b/compiler/src/dmd/expressionsem.d
@@ -3074,9 +3074,15 @@ private bool functionParameters(Loc loc, Scope* sc,
                 return errorArgs();
             }
             arg = p.defaultArg;
+
             if (!arg.type)
                 arg = arg.expressionSemantic(sc);
             arg = inlineCopy(arg, sc);
+            // see https://github.com/dlang/dmd/issues/21409
+            // default arg can contain a VarExp that's for a VarDecl
+            // located in another FuncDecl that the one the CallExp is located in
+            lambdaCheckForNestedRef(arg, sc);
+
             // __FILE__, __LINE__, __MODULE__, __FUNCTION__, and __PRETTY_FUNCTION__
             arg = arg.resolveLoc(loc, sc);
             if (i >= nargs)
diff --git a/compiler/test/runnable/issue21409.d b/compiler/test/runnable/issue21409.d
new file mode 100644
index 000000000000..04bf3e805843
--- /dev/null
+++ b/compiler/test/runnable/issue21409.d
@@ -0,0 +1,102 @@
+module issue21409;
+
+void test1()
+{
+    uint p0 = 8;
+    uint p1 = 9;
+
+    static void f1(uint c0 = p0, uint c1 = p1)
+    {
+        assert(c0 + c1 == 17); // fails
+    }
+
+    void f0()
+    {
+        /* uncomment to remind the compiler
+        it has to create a closure for p0 and p1 */
+        // if (p0 || p1) {}
+
+        f1();
+    }
+
+    f0();
+}
+
+void test2()
+{
+    struct S
+    {
+        uint p0 = 18;
+        uint p1 = 1;
+    }
+    S s;
+
+    static void f1(uint c0 = s.p0, uint c1 = s.p1)
+    {
+        assert(c0 + c1 == 19); // fails
+    }
+
+    void f0()
+    {
+        f1();
+    }
+
+    f0();
+}
+
+void test3()
+{
+    uint p0 = 8;
+    uint p1 = 9;
+
+    static void f1(uint c0 = p0 + 1, uint c1 = p1)
+    {
+        assert(c0 + c1 == 18); // fails
+    }
+
+    void f0()
+    {
+        /* uncomment to remind the compiler
+        it has to create a closure for p0 and p1 */
+        // if (p0 || p1) {}
+
+        f1();
+    }
+
+    f0();
+}
+
+// see InlineCostVisitor.visit(ThisExp)
+/*void test4()
+{
+    struct S
+    {
+        uint p0 = 18;
+        uint p1 = 1;
+
+        void test()
+        {
+            static void f3(S vthis = this)
+            {
+                assert(vthis.p0 + vthis.p1 == 19);
+            }
+
+            void f2()
+            {
+                f3();
+            }
+
+            f2();
+        }
+    }
+    S s;
+    s.test();
+}*/
+
+void main()
+{
+    test1();
+    test2();
+    test3();
+    //test4();
+}