diff --git a/llvm/test/TableGen/DecoderEmitter/large-islands.td b/llvm/test/TableGen/DecoderEmitter/large-islands.td
new file mode 100644
index 000000000000..541cba495dc3
--- /dev/null
+++ b/llvm/test/TableGen/DecoderEmitter/large-islands.td
@@ -0,0 +1,38 @@
+// RUN: llvm-tblgen -gen-disassembler -I %p/../../../include %s | FileCheck %s
+
+include "llvm/Target/Target.td"
+
+class I<dag outs, dag ins, bits<5> opcode> : Instruction {
+  let InOperandList = ins;
+  let OutOperandList = outs;
+
+  bits<5> dst;
+  bits<5> src0;
+  bits<5> src1;
+
+  int Size = 16;
+  bits<128> Inst;
+
+  let Inst{4...0} = opcode;
+  let Inst{9...5} = dst;
+  let Inst{14...10} = src0;
+  let Inst{19...15} = src1;
+
+  let Inst{127...20} = 0xdeadbeef;
+}
+
+def Reg : Register<"reg">;
+
+def Regs : RegisterClass<"foo", [i32], 0, (add Reg)>;
+
+def IAdd : I<(outs Regs:$dst), (ins Regs:$src0, Regs:$src1), 0b10101>;
+
+// CHECK-LABEL: static const uint8_t DecoderTable128[20] = {
+// CHECK-NEXT:   OPC_CheckField, 84, 44, 0,                 //  0: check Inst[127:84] == 0x0
+// CHECK-NEXT:   OPC_CheckField, 20, 64, 239, 253, 182, 245, 13, 
+
+def II : InstrInfo;
+
+def MyTarget : Target {
+  let InstructionSet = II;
+}
diff --git a/llvm/utils/TableGen/DecoderEmitter.cpp b/llvm/utils/TableGen/DecoderEmitter.cpp
index 5d41b7dc3c31..664c3009ff50 100644
--- a/llvm/utils/TableGen/DecoderEmitter.cpp
+++ b/llvm/utils/TableGen/DecoderEmitter.cpp
@@ -656,8 +656,14 @@ static std::vector<EncodingIsland> getIslands(const KnownBits &EncodingBits,
     if (!IsFiltered && IsKnown) {
       if (OnIsland) {
         // Accumulate island bits.
-        FieldVal |= static_cast<uint64_t>(EncodingBits.One[I])
-                    << (I - StartBit);
+        const unsigned BitNo = I - StartBit;
+        FieldVal |= static_cast<uint64_t>(EncodingBits.One[I]) << (BitNo);
+        // If island becomes larger than 64-bits complete the island and start a
+        // new one
+        if (BitNo >= 63) {
+          Islands.push_back({StartBit, 64, FieldVal});
+          OnIsland = false;
+        }
       } else {
         // Onto an island.
         StartBit = I;