diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index f8de2b4..0f76136 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -1958,10 +1958,16 @@
     Width = Info.Width;
     Align = Info.Align;
 
-    // If the size of the type doesn't exceed the platform's max
-    // atomic promotion width, make the size and alignment more
-    // favorable to atomic operations:
-    if (Width != 0 && Width <= Target->getMaxAtomicPromoteWidth()) {
+    if (!Width) {
+      // An otherwise zero-sized type should still generate an
+      // atomic operation.
+      Width = Target->getCharWidth();
+      assert(Align);
+    } else if (Width <= Target->getMaxAtomicPromoteWidth()) {
+      // If the size of the type doesn't exceed the platform's max
+      // atomic promotion width, make the size and alignment more
+      // favorable to atomic operations:
+
       // Round the size up to a power of 2.
       if (!llvm::isPowerOf2_64(Width))
         Width = llvm::NextPowerOf2(Width);