diff --git a/opcodes/ChangeLog b/opcodes/ChangeLog
index 47873949c7..63560f11cb 100644
--- a/opcodes/ChangeLog
+++ b/opcodes/ChangeLog
@@ -1,3 +1,8 @@
+2018-11-29  Jim Wilson  <jimw@sifive.com>
+
+	* riscv-opc.c (unimp): Mark compressed unimp as INSN_ALIAS.
+	(c.unimp): New.
+
 2018-11-27  Jim Wilson  <jimw@sifive.com>
 
 	* riscv-opc.c (ciw): Fix whitespace to align columns.
diff --git a/opcodes/riscv-opc.c b/opcodes/riscv-opc.c
index a272e29fee..3da2a7702b 100644
--- a/opcodes/riscv-opc.c
+++ b/opcodes/riscv-opc.c
@@ -198,7 +198,7 @@ match_srxi_as_c_srxi (const struct riscv_opcode *op, insn_t insn)
 const struct riscv_opcode riscv_opcodes[] =
 {
 /* name,     xlen, isa,   operands, match, mask, match_func, pinfo.  */
-{"unimp",       0, {"C", 0},   "",  0, 0xffffU,  match_opcode, 0 },
+{"unimp",       0, {"C", 0},   "",  0, 0xffffU,  match_opcode, INSN_ALIAS },
 {"unimp",       0, {"I", 0},   "",  MATCH_CSRRW | (CSR_CYCLE << OP_SH_CSR), 0xffffffffU,  match_opcode, 0 }, /* csrw cycle, x0 */
 {"ebreak",      0, {"C", 0},   "",  MATCH_C_EBREAK, MASK_C_EBREAK, match_opcode, INSN_ALIAS },
 {"ebreak",      0, {"I", 0},   "",    MATCH_EBREAK, MASK_EBREAK, match_opcode, 0 },
@@ -696,6 +696,7 @@ const struct riscv_opcode riscv_opcodes[] =
 {"fcvt.q.lu", 64, {"Q", 0}, "D,s,m",  MATCH_FCVT_Q_LU, MASK_FCVT_Q_LU, match_opcode, 0 },
 
 /* Compressed instructions.  */
+{"c.unimp",    0, {"C", 0},   "",  0, 0xffffU,  match_opcode, 0 },
 {"c.ebreak",   0, {"C", 0},   "",  MATCH_C_EBREAK, MASK_C_EBREAK, match_opcode, 0 },
 {"c.jr",       0, {"C", 0},   "d",  MATCH_C_JR, MASK_C_JR, match_rd_nonzero, INSN_BRANCH },
 {"c.jalr",     0, {"C", 0},   "d",  MATCH_C_JALR, MASK_C_JALR, match_rd_nonzero, INSN_JSR },