Index: include/clang/Analysis/Analyses/FormatString.h
===================================================================
--- include/clang/Analysis/Analyses/FormatString.h
+++ include/clang/Analysis/Analyses/FormatString.h
@@ -257,17 +257,21 @@
   const Kind K;
   QualType T;
   const char *Name;
-  bool Ptr;
+  bool Ptr, IsSizeT;
+
 public:
   ArgType(Kind k = UnknownTy, const char *n = nullptr)
-      : K(k), Name(n), Ptr(false) {}
+      : K(k), Name(n), Ptr(false), IsSizeT(false) {}
   ArgType(QualType t, const char *n = nullptr)
-      : K(SpecificTy), T(t), Name(n), Ptr(false) {}
-  ArgType(CanQualType t) : K(SpecificTy), T(t), Name(nullptr), Ptr(false) {}
+      : K(SpecificTy), T(t), Name(n), Ptr(false), IsSizeT(false) {}
+  ArgType(CanQualType t)
+      : K(SpecificTy), T(t), Name(nullptr), Ptr(false), IsSizeT(false) {}
 
   static ArgType Invalid() { return ArgType(InvalidTy); }
   bool isValid() const { return K != InvalidTy; }
 
+  bool isSizeT() const { return IsSizeT; }
+
   /// Create an ArgType which corresponds to the type pointer to A.
   static ArgType PtrTo(const ArgType& A) {
     assert(A.K >= InvalidTy && "ArgType cannot be pointer to invalid/unknown");
@@ -276,6 +280,13 @@
     return Res;
   }
 
+  /// Create an ArgType which corresponds to the size_t/ssize_t type.
+  static ArgType makeSizeT(const ArgType &A) {
+    ArgType Res = A;
+    Res.IsSizeT = true;
+    return Res;
+  }
+
   MatchKind matchesType(ASTContext &C, QualType argTy) const;
 
   QualType getRepresentativeType(ASTContext &C) const;
Index: lib/Analysis/PrintfFormatString.cpp
===================================================================
--- lib/Analysis/PrintfFormatString.cpp
+++ lib/Analysis/PrintfFormatString.cpp
@@ -466,7 +466,7 @@
       case LengthModifier::AsIntMax:
         return ArgType(Ctx.getIntMaxType(), "intmax_t");
       case LengthModifier::AsSizeT:
-        return ArgType(Ctx.getSignedSizeType(), "ssize_t");
+        return ArgType::makeSizeT(ArgType(Ctx.getSignedSizeType(), "ssize_t"));
       case LengthModifier::AsInt3264:
         return Ctx.getTargetInfo().getTriple().isArch64Bit()
                    ? ArgType(Ctx.LongLongTy, "__int64")
@@ -499,7 +499,7 @@
       case LengthModifier::AsIntMax:
         return ArgType(Ctx.getUIntMaxType(), "uintmax_t");
       case LengthModifier::AsSizeT:
-        return ArgType(Ctx.getSizeType(), "size_t");
+        return ArgType::makeSizeT(ArgType(Ctx.getSizeType(), "size_t"));
       case LengthModifier::AsInt3264:
         return Ctx.getTargetInfo().getTriple().isArch64Bit()
                    ? ArgType(Ctx.UnsignedLongLongTy, "unsigned __int64")
Index: lib/Sema/SemaChecking.cpp
===================================================================
--- lib/Sema/SemaChecking.cpp
+++ lib/Sema/SemaChecking.cpp
@@ -6374,6 +6374,11 @@
     QualType CastTy;
     std::tie(CastTy, CastTyName) = shouldNotPrintDirectly(S.Context, IntendedTy, E);
     if (!CastTy.isNull()) {
+      // %zi/%zu are ok to use for NSInteger/NSUInteger of type int
+      // (long in ASTContext).
+      if ((CastTyName == "NSInteger" || CastTyName == "NSUInteger") &&
+          AT.isSizeT() && AT.matchesType(S.Context, CastTy))
+        return true;
       IntendedTy = CastTy;
       ShouldNotPrintDirectly = true;
     }
Index: test/SemaObjC/format-size-spec-nsinteger.m
===================================================================
--- /dev/null
+++ test/SemaObjC/format-size-spec-nsinteger.m
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -triple thumbv7-apple-ios -Wformat -fsyntax-only -fblocks -verify -Wno-objc-root-class %s
+// RUN: %clang_cc1 -triple arm64-apple-ios -Wformat -fsyntax-only -fblocks -verify -Wno-objc-root-class %s
+// expected-no-diagnostics
+
+#if __LP64__
+typedef unsigned long NSUInteger;
+typedef long NSInteger;
+#else
+typedef unsigned int NSUInteger;
+typedef int NSInteger;
+#endif
+
+@class NSString;
+
+extern void NSLog(NSString *format, ...);
+
+void testSizeSpecifier() {
+  NSInteger i = 0;
+  NSUInteger j = 0;
+  NSLog(@"max NSInteger = %zi", i);
+  NSLog(@"max NSUinteger = %zu", j);
+}