diff --git a/lib/Target/ARM/Disassembler/ARMDisassembler.cpp b/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
index 0e27e16f941..1c9d95fb08a 100644
--- a/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
+++ b/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
@@ -508,17 +508,23 @@ bool ThumbDisassembler::getInstruction(MCInst &MI,
 }
 
 // A8.6.50
+// Valid return values are {1, 2, 3, 4}, with 0 signifying an error condition.
 static unsigned short CountITSize(unsigned ITMask) {
   // First count the trailing zeros of the IT mask.
   unsigned TZ = CountTrailingZeros_32(ITMask);
-  assert(TZ <= 3 && "Encoding error");
+  if (TZ > 3) {
+    DEBUG(errs() << "Encoding error of IT mask");
+    return 0;
+  }
   return (4 - TZ);
 }
 
-/// Init ITState.
-void Session::InitIT(unsigned short bits7_0) {
+/// Init ITState.  Note that at least one bit is always 1 in mask.
+bool Session::InitIT(unsigned short bits7_0) {
   ITCounter = CountITSize(slice(bits7_0, 3, 0));
   ITState = bits7_0;
+  // Only need to check for > 0.
+  return ITCounter > 0;
 }
 
 /// Update ITState if necessary.
diff --git a/lib/Target/ARM/Disassembler/ARMDisassembler.h b/lib/Target/ARM/Disassembler/ARMDisassembler.h
index e418b2ba51e..0a74a3866ee 100644
--- a/lib/Target/ARM/Disassembler/ARMDisassembler.h
+++ b/lib/Target/ARM/Disassembler/ARMDisassembler.h
@@ -60,7 +60,7 @@ public:
   Session() : ITCounter(0), ITState(0) {}
   ~Session() {}
   /// InitIT - Initializes ITCounter/ITState.
-  void InitIT(unsigned short bits7_0);
+  bool InitIT(unsigned short bits7_0);
   /// UpdateIT - Updates ITCounter/ITState as IT Block progresses.
   void UpdateIT();
 
diff --git a/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp b/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp
index c261948d909..6e76200b35e 100644
--- a/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp
+++ b/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp
@@ -3282,7 +3282,7 @@ bool ARMBasicMCBuilder::RunBuildAfterHook(bool Status, MCInst &MI,
   if (!SP) return Status;
 
   if (Opcode == ARM::t2IT)
-    SP->InitIT(slice(insn, 7, 0));
+    Status = SP->InitIT(slice(insn, 7, 0)) ? Status : false;
   else if (InITBlock())
     SP->UpdateIT();