diff --git a/libcxx/test/std/experimental/memory/memory.resource.global/new_delete_resource.pass.cpp b/libcxx/test/std/experimental/memory/memory.resource.global/new_delete_resource.pass.cpp
--- a/libcxx/test/std/experimental/memory/memory.resource.global/new_delete_resource.pass.cpp
+++ b/libcxx/test/std/experimental/memory/memory.resource.global/new_delete_resource.pass.cpp
@@ -25,14 +25,14 @@
 struct assert_on_compare : public ex::memory_resource
 {
 protected:
-    virtual void * do_allocate(size_t, size_t)
-    { assert(false); }
+    void * do_allocate(size_t, size_t) override
+    { assert(false); return nullptr; }
 
-    virtual void do_deallocate(void *, size_t, size_t)
+    void do_deallocate(void *, size_t, size_t) override
     { assert(false); }
 
-    virtual bool do_is_equal(ex::memory_resource const &) const noexcept
-    { assert(false); }
+    bool do_is_equal(ex::memory_resource const &) const noexcept override
+    { assert(false); return false; }
 };
 
 void test_return()
diff --git a/libcxx/test/std/experimental/memory/memory.resource.global/null_memory_resource.pass.cpp b/libcxx/test/std/experimental/memory/memory.resource.global/null_memory_resource.pass.cpp
--- a/libcxx/test/std/experimental/memory/memory.resource.global/null_memory_resource.pass.cpp
+++ b/libcxx/test/std/experimental/memory/memory.resource.global/null_memory_resource.pass.cpp
@@ -25,14 +25,14 @@
 struct assert_on_compare : public ex::memory_resource
 {
 protected:
-    virtual void * do_allocate(size_t, size_t)
-    { assert(false); }
+    void * do_allocate(size_t, size_t) override
+    { assert(false); return nullptr; }
 
-    virtual void do_deallocate(void *, size_t, size_t)
+    void do_deallocate(void *, size_t, size_t) override
     { assert(false); }
 
-    virtual bool do_is_equal(ex::memory_resource const &) const noexcept
-    { assert(false); }
+    bool do_is_equal(ex::memory_resource const &) const noexcept override
+    { assert(false); return false; }
 };
 
 void test_return()