Index: lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
===================================================================
--- lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
+++ lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
@@ -212,6 +212,15 @@
 }
 
 template <unsigned N>
+static DecodeStatus decodeUImmNonZeroOperand(MCInst &Inst, uint64_t Imm,
+                                             int64_t Address,
+                                             const void *Decoder) {
+  if (Imm == 0)
+    return MCDisassembler::Fail;
+  return decodeUImmOperand<N>(Inst, Imm, Address, Decoder);
+}
+
+template <unsigned N>
 static DecodeStatus decodeSImmOperand(MCInst &Inst, uint64_t Imm,
                                       int64_t Address, const void *Decoder) {
   assert(isUInt<N>(Imm) && "Invalid immediate");
Index: lib/Target/RISCV/RISCVInstrInfoC.td
===================================================================
--- lib/Target/RISCV/RISCVInstrInfoC.td
+++ lib/Target/RISCV/RISCVInstrInfoC.td
@@ -167,7 +167,7 @@
                           [{return isShiftedUInt<8, 2>(Imm) && (Imm != 0);}]> {
   let ParserMatchClass = UImmAsmOperand<10, "Lsb00NonZero">;
   let EncoderMethod = "getImmOpValue";
-  let DecoderMethod = "decodeUImmOperand<10>";
+  let DecoderMethod = "decodeUImmNonZeroOperand<10>";
   let MCOperandPredicate = [{
     int64_t Imm;
     if (!MCOp.evaluateAsConstantImm(Imm))
Index: test/MC/Disassembler/RISCV/illegal-instruction.txt
===================================================================
--- /dev/null
+++ test/MC/Disassembler/RISCV/illegal-instruction.txt
@@ -0,0 +1,9 @@
+# RUN: not llvm-mc -disassemble -triple=riscv32 -mattr=+c < %s 2>&1 | FileCheck %s
+# RUN: not llvm-mc -disassemble -triple=riscv64 -mattr=+c < %s 2>&1 | FileCheck %s
+#
+# Test generated by a LLVM MC Disassembler Protocol Buffer Fuzzer
+# for the RISC-V assembly language.
+
+# This should not decode as c.addi4spn with 0 imm when compression is enabled.
+[0x00 0x00]
+# CHECK: warning: invalid instruction encoding