diff --git a/compiler/src/dmd/func.d b/compiler/src/dmd/func.d
index 25987a7819..88e7aeea95 100644
--- a/compiler/src/dmd/func.d
+++ b/compiler/src/dmd/func.d
@@ -820,15 +820,13 @@ extern (C++) class FuncDeclaration : Declaration
     bool addPreInvariant()
     {
         auto ad = isThis();
-        ClassDeclaration cd = ad ? ad.isClassDeclaration() : null;
-        return (ad && !(cd && cd.isCPPclass()) && global.params.useInvariants == CHECKENABLE.on && (visibility.kind == Visibility.Kind.protected_ || visibility.kind == Visibility.Kind.public_ || visibility.kind == Visibility.Kind.export_) && !this.isNaked());
+        return (ad && global.params.useInvariants == CHECKENABLE.on && (visibility.kind == Visibility.Kind.protected_ || visibility.kind == Visibility.Kind.public_ || visibility.kind == Visibility.Kind.export_) && !this.isNaked());
     }
 
     bool addPostInvariant()
     {
         auto ad = isThis();
-        ClassDeclaration cd = ad ? ad.isClassDeclaration() : null;
-        return (ad && !(cd && cd.isCPPclass()) && ad.inv && global.params.useInvariants == CHECKENABLE.on && (visibility.kind == Visibility.Kind.protected_ || visibility.kind == Visibility.Kind.public_ || visibility.kind == Visibility.Kind.export_) && !this.isNaked());
+        return (ad && ad.inv && global.params.useInvariants == CHECKENABLE.on && (visibility.kind == Visibility.Kind.protected_ || visibility.kind == Visibility.Kind.public_ || visibility.kind == Visibility.Kind.export_) && !this.isNaked());
     }
 
     override const(char)* kind() const
diff --git a/compiler/test/runnable/testinvariant.d b/compiler/test/runnable/testinvariant.d
index 0ce8557191..11b8829b9f 100644
--- a/compiler/test/runnable/testinvariant.d
+++ b/compiler/test/runnable/testinvariant.d
@@ -228,8 +228,52 @@ void test16384()
     assert(s == "needs to be thrown2");
 }
 
-
 /***************************************************/
+// Fix: https://github.com/dlang/dmd/issues/20924 (invariant not called on extern(C++) classes)
+
+extern(C++) class C
+{
+    invariant { assert(0); }
+    void f() {}
+}
+
+extern(D) class D
+{
+    invariant { assert(0); }
+    void f() {}
+}
+
+void test20924()
+{
+    import core.exception : AssertError;
+    // Test extern(C++) class invariant
+    try
+    {
+        auto c = new C();
+        c.f(); // Trigger invariant
+        assert(false, "Failed: invariant in extern(C++) class not checked");
+    }
+    catch (AssertError e)
+    {
+        // Expected behavior - invariant was checked
+        return;
+    }
+    assert(0, "Invariant in extern(C++) class was not checked");
+
+    // Test extern(D) class invariant
+    try
+    {
+        auto d = new D();
+        d.f(); // Trigger invariant
+        assert(false, "Failed: invariant in extern(D) class not checked");
+    }
+    catch (AssertError e)
+    {
+        // Expected behavior - invariant was checked
+        return;
+    }
+    assert(0, "Invariant in extern(D) class was not checked");
+}
 
 void main()
 {
@@ -238,4 +282,5 @@ void main()
     test16384();
     test13113();
     test13147();
+    test20924();
 }