diff --git a/gas/config/tc-riscv.c b/gas/config/tc-riscv.c
index 3355bfbbfb2..f90ce0a6650 100644
--- a/gas/config/tc-riscv.c
+++ b/gas/config/tc-riscv.c
@@ -1110,7 +1110,7 @@ validate_riscv_insn (const struct riscv_opcode *opc, int length)
   else
     insn_width = 8 * length;
 
-  required_bits = ~0ULL >> (64 - insn_width);
+  required_bits = ((insn_t)~0ULL) >> (64 - insn_width);
 
   if ((used_bits & opc->match) != (opc->match & required_bits))
     {