Index: lib/Sema/SemaChecking.cpp
===================================================================
--- lib/Sema/SemaChecking.cpp
+++ lib/Sema/SemaChecking.cpp
@@ -7709,6 +7709,30 @@
   return std::make_pair(QualType(), StringRef());
 }
 
+/// Return true if \p ICE is an implicit argument promotion of an arithmetic
+/// type. Bit-field 'promotions' from a higher ranked type to a lower ranked
+/// type do not count.
+static bool
+isArithmeticArgumentPromotion(Sema &S, const ImplicitCastExpr *ICE) {
+  QualType From = ICE->getSubExpr()->getType();
+  QualType To = ICE->getType();
+  // It's an integer promotion if the destination type is the promoted
+  // source type.
+  if (ICE->getCastKind() == CK_IntegralCast &&
+      From->isPromotableIntegerType() &&
+      S.Context.getPromotedIntegerType(From) == To)
+    return true;
+  // Look through vector types, since we do default argument promotion for
+  // those in OpenCL.
+  if (const auto *VecTy = From->getAs<ExtVectorType>())
+    From = VecTy->getElementType();
+  if (const auto *VecTy = To->getAs<ExtVectorType>())
+    To = VecTy->getElementType();
+  // It's a floating promotion if the source type is a lower rank.
+  return ICE->getCastKind() == CK_FloatingCast &&
+         S.Context.getFloatingTypeOrder(From, To) < 0;
+}
+
 bool
 CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
                                     const char *StartSpecifier,
@@ -7736,11 +7760,11 @@
 
   // Look through argument promotions for our error message's reported type.
   // This includes the integral and floating promotions, but excludes array
-  // and function pointer decay; seeing that an argument intended to be a
-  // string has type 'char [6]' is probably more confusing than 'char *'.
+  // and function pointer decay (seeing that an argument intended to be a
+  // string has type 'char [6]' is probably more confusing than 'char *') and
+  // certain bitfield promotions (bitfields can be 'demoted' to a lesser type).
   if (const ImplicitCastExpr *ICE = dyn_cast<ImplicitCastExpr>(E)) {
-    if (ICE->getCastKind() == CK_IntegralCast ||
-        ICE->getCastKind() == CK_FloatingCast) {
+    if (isArithmeticArgumentPromotion(S, ICE)) {
       E = ICE->getSubExpr();
       ExprTy = E->getType();
 
Index: test/Sema/format-strings-bitfield-promotion.c
===================================================================
--- /dev/null
+++ test/Sema/format-strings-bitfield-promotion.c
@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple x86_64-unknown-windows-msvc -fsyntax-only -verify %s
+
+int printf(const char *restrict, ...);
+
+struct bitfields {
+  long a : 2;
+  unsigned long b : 2;
+  long c : 32;          // assumes that int is 32 bits
+  unsigned long d : 32; // assumes that int is 32 bits
+} bf;
+
+void bitfield_promotion() {
+  printf("%ld", bf.a); // expected-warning {{format specifies type 'long' but the argument has type 'int'}}
+  printf("%lu", bf.b); // expected-warning {{format specifies type 'unsigned long' but the argument has type 'int'}}
+  printf("%ld", bf.c); // expected-warning {{format specifies type 'long' but the argument has type 'int'}}
+  printf("%lu", bf.d); // expected-warning {{format specifies type 'unsigned long' but the argument has type 'unsigned int'}}
+}
Index: test/Sema/format-strings-bitfield-promotion.cxx
===================================================================
--- /dev/null
+++ test/Sema/format-strings-bitfield-promotion.cxx
@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple x86_64-unknown-windows-msvc -fsyntax-only -verify %s
+
+// In C++, the bitfield promotion from long to int does not occur, unlike C.
+// expected-no-diagnostics
+
+int printf(const char *restrict, ...);
+
+struct bitfields {
+  long a : 2;
+  unsigned long b : 2;
+  long c : 32;          // assumes that int is 32 bits
+  unsigned long d : 32; // assumes that int is 32 bits
+} bf;
+
+void bitfield_promotion() {
+  printf("%ld", bf.a);
+  printf("%lu", bf.b);
+  printf("%ld", bf.c);
+  printf("%lu", bf.d);
+}