diff --git a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 31cb0cab580..f000a7063d5 100644
--- a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -283,6 +283,8 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
   // Handle the zerofill directive on darwin, which is a special form of BSS
   // emission.
   if (GVKind.isBSSExtern() && MAI->hasMachoZeroFillDirective()) {
+    if (Size == 0) Size = 1;  // zerofill of 0 bytes is undefined.
+    
     // .globl _foo
     OutStreamer.EmitSymbolAttribute(GVSym, MCSA_Global);
     // .zerofill __DATA, __common, _foo, 400, 5
diff --git a/test/CodeGen/X86/global-sections.ll b/test/CodeGen/X86/global-sections.ll
index 732d764dbde..6d211913b01 100644
--- a/test/CodeGen/X86/global-sections.ll
+++ b/test/CodeGen/X86/global-sections.ll
@@ -144,3 +144,17 @@
 ; LINUX: G10:
 ; LINUX:	.zero	400
 
+
+
+;; Zero sized objects should round up to 1 byte in zerofill directives.
+; rdar://7886017
+@G11 = global [0 x i32] zeroinitializer
+@G12 = global {} zeroinitializer
+@G13 = global { [0 x {}] } zeroinitializer
+
+; DARWIN: .globl _G11
+; DARWIN: .zerofill __DATA,__common,_G11,1,2
+; DARWIN: .globl _G12
+; DARWIN: .zerofill __DATA,__common,_G12,1,3
+; DARWIN: .globl _G13
+; DARWIN: .zerofill __DATA,__common,_G13,1,3