diff --git a/lib/Target/ARM/ARMInstrThumb2.td b/lib/Target/ARM/ARMInstrThumb2.td
index 1684339d6f5..94bc23eb775 100644
--- a/lib/Target/ARM/ARMInstrThumb2.td
+++ b/lib/Target/ARM/ARMInstrThumb2.td
@@ -3245,11 +3245,11 @@ def t2B   : T2I<(outs), (ins uncondbrtarget:$target), IIC_Br,
   let Inst{15-14} = 0b10;
   let Inst{12} = 1;
 
-  bits<20> target;
+  bits<24> target;
   let Inst{26} = target{19};
   let Inst{11} = target{18};
   let Inst{13} = target{17};
-  let Inst{21-16} = target{16-11};
+  let Inst{25-16} = target{20-11};
   let Inst{10-0} = target{10-0};
   let DecoderMethod = "DecodeT2BInstruction";
 }
diff --git a/lib/Target/ARM/Disassembler/ARMDisassembler.cpp b/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
index d2b1cc37f21..f00142de50d 100644
--- a/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
+++ b/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
@@ -2095,16 +2095,28 @@ static DecodeStatus DecodeAddrMode7Operand(MCInst &Inst, unsigned Val,
 static DecodeStatus
 DecodeT2BInstruction(MCInst &Inst, unsigned Insn,
                      uint64_t Address, const void *Decoder) {
-  DecodeStatus S = MCDisassembler::Success;
-  unsigned imm = (fieldFromInstruction(Insn, 0, 11) << 0) |
-                 (fieldFromInstruction(Insn, 11, 1) << 18) |
-                 (fieldFromInstruction(Insn, 13, 1) << 17) |
-                 (fieldFromInstruction(Insn, 16, 6) << 11) |
-                 (fieldFromInstruction(Insn, 26, 1) << 19);
-  if (!tryAddingSymbolicOperand(Address, Address + SignExtend32<20>(imm<<1) + 4,
+  DecodeStatus Status = MCDisassembler::Success;
+
+  // Note the J1 and J2 values are from the encoded instruction.  So here
+  // change them to I1 and I2 values via as documented:
+  // I1 = NOT(J1 EOR S);
+  // I2 = NOT(J2 EOR S);
+  // and build the imm32 with one trailing zero as documented:
+  // imm32 = SignExtend(S:I1:I2:imm10:imm11:'0', 32);
+  unsigned S = fieldFromInstruction(Insn, 26, 1);
+  unsigned J1 = fieldFromInstruction(Insn, 13, 1);
+  unsigned J2 = fieldFromInstruction(Insn, 11, 1);
+  unsigned I1 = !(J1 ^ S);
+  unsigned I2 = !(J2 ^ S);
+  unsigned imm10 = fieldFromInstruction(Insn, 16, 10);
+  unsigned imm11 = fieldFromInstruction(Insn, 0, 11);
+  unsigned tmp = (S << 23) | (I1 << 22) | (I2 << 21) | (imm10 << 11) | imm11;
+  int imm32 = SignExtend32<24>(tmp << 1);
+  if (!tryAddingSymbolicOperand(Address, Address + imm32 + 4,
                                 true, 4, Inst, Decoder))
-    Inst.addOperand(MCOperand::CreateImm(SignExtend32<20>(imm << 1)));
-  return S;
+    Inst.addOperand(MCOperand::CreateImm(imm32));
+
+  return Status;
 }
 
 static DecodeStatus
diff --git a/test/MC/ARM/thumb2-b.w-encodingT4.s b/test/MC/ARM/thumb2-b.w-encodingT4.s
new file mode 100644
index 00000000000..be77b06267a
--- /dev/null
+++ b/test/MC/ARM/thumb2-b.w-encodingT4.s
@@ -0,0 +1,12 @@
+@ RUN: llvm-mc -triple=thumbv7-apple-darwin -mcpu=cortex-a8 -show-encoding < %s | FileCheck %s
+  .syntax unified
+  .globl _func
+.thumb_func _foo
+.space 0x37c6
+_foo:
+@------------------------------------------------------------------------------
+@ B (thumb2 b.w encoding T4) rdar://12585795
+@------------------------------------------------------------------------------
+        b.w   0x3680c
+
+@ CHECK: b.w	#223244                    @ encoding: [0x6d,0xf0,0x0c,0xb0]
diff --git a/test/MC/Disassembler/ARM/thumb2.txt b/test/MC/Disassembler/ARM/thumb2.txt
index 42ebe58207b..45dace3b09c 100644
--- a/test/MC/Disassembler/ARM/thumb2.txt
+++ b/test/MC/Disassembler/ARM/thumb2.txt
@@ -169,6 +169,9 @@
 
 0x13 0xf5 0xce 0xa9
 
+# CHECK: b.w   #208962
+
+0x33 0xf0 0x21 0xb8 # rdar://12585795
 
 #------------------------------------------------------------------------------
 # BFC