Index: cfe/trunk/lib/Analysis/PrintfFormatString.cpp
===================================================================
--- cfe/trunk/lib/Analysis/PrintfFormatString.cpp
+++ cfe/trunk/lib/Analysis/PrintfFormatString.cpp
@@ -466,8 +466,7 @@
       case LengthModifier::AsIntMax:
         return ArgType(Ctx.getIntMaxType(), "intmax_t");
       case LengthModifier::AsSizeT:
-        // FIXME: How to get the corresponding signed version of size_t?
-        return ArgType();
+        return ArgType(Ctx.getSignedSizeType(), "ssize_t");
       case LengthModifier::AsInt3264:
         return Ctx.getTargetInfo().getTriple().isArch64Bit()
                    ? ArgType(Ctx.LongLongTy, "__int64")
@@ -537,7 +536,7 @@
       case LengthModifier::AsIntMax:
         return ArgType::PtrTo(ArgType(Ctx.getIntMaxType(), "intmax_t"));
       case LengthModifier::AsSizeT:
-        return ArgType(); // FIXME: ssize_t
+        return ArgType::PtrTo(ArgType(Ctx.getSignedSizeType(), "ssize_t"));
       case LengthModifier::AsPtrDiff:
         return ArgType::PtrTo(ArgType(Ctx.getPointerDiffType(), "ptrdiff_t"));
       case LengthModifier::AsLongDouble:
Index: cfe/trunk/test/FixIt/format.m
===================================================================
--- cfe/trunk/test/FixIt/format.m
+++ cfe/trunk/test/FixIt/format.m
@@ -229,6 +229,19 @@
   // CHECK: fix-it:"{{.*}}":{[[@LINE-2]]:11-[[@LINE-2]]:14}:"%+ld"
 }
 
+void testSizeTypes() {
+  printf("%zu", 0.f); // expected-warning{{format specifies type 'size_t' (aka 'unsigned long') but the argument has type 'float'}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:11-[[@LINE-1]]:14}:"%f"
+
+  printf("%zd", 0.f); // expected-warning{{format specifies type 'ssize_t' (aka 'long') but the argument has type 'float'}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:11-[[@LINE-1]]:14}:"%f"
+  
+  int x;
+  printf("%zn", &x); // expected-warning{{format specifies type 'ssize_t *' (aka 'long *') but the argument has type 'int *'}}
+  // PrintfSpecifier::fixType doesn't handle %n, so a fix-it is not emitted, 
+  // see the comment in PrintfSpecifier::fixType in PrintfFormatString.cpp.
+}
+
 void testEnum() {
   typedef enum {
     ImplicitA = 1,