diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -202,6 +202,8 @@
 - Fix crash when evaluating consteval constructor of derived class whose base
   has more than one field.
   (`#60166 <https://github.com/llvm/llvm-project/issues/60166>`_)
+- Fix incorrect deletion of the default constructor of unions in some
+  cases. (`#48416 <https://github.com/llvm/llvm-project/issues/48416>`_)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -9157,7 +9157,15 @@
     // must be accessible and non-deleted, but need not be trivial. Such a
     // destructor is never actually called, but is semantically checked as
     // if it were.
-    DiagKind = 4;
+    if (CSM == Sema::CXXDefaultConstructor) {
+      // Default constructor of a union can also be valid if one of the
+      // members has an explicit initializer.
+      auto* RD = dyn_cast<CXXRecordDecl>(Field->getParent());
+      assert(RD);
+      if (!RD->hasInClassInitializer())
+        DiagKind = 4;
+    } else
+      DiagKind = 4;
   }
 
   if (DiagKind == -1)
diff --git a/clang/test/SemaCXX/cxx0x-nontrivial-union.cpp b/clang/test/SemaCXX/cxx0x-nontrivial-union.cpp
--- a/clang/test/SemaCXX/cxx0x-nontrivial-union.cpp
+++ b/clang/test/SemaCXX/cxx0x-nontrivial-union.cpp
@@ -144,3 +144,37 @@
 
   Test2<X> t2x;  // expected-error {{call to implicitly-deleted default constructor of 'Test2<X>'}}
 }
+
+namespace GH48416 {
+
+struct non_trivial_constructor {
+    non_trivial_constructor() {}
+};
+
+
+union U1 {
+    int a;
+    non_trivial_constructor b; // expected-note {{has a non-trivial default constructor}}
+};
+
+union U2 {
+    int a{};
+    non_trivial_constructor b;
+};
+
+union U3 {
+    int a;
+    non_trivial_constructor b{};
+};
+
+union U4 {
+    int a{}; // expected-note {{previous initialization is here}}
+    non_trivial_constructor b{}; // expected-error {{initializing multiple members of union}}
+};
+
+U1 u1; // expected-error {{call to implicitly-deleted default constructor}}
+U2 u2;
+U3 u3;
+U4 u4;
+
+} // namespace GH48416