diff --git a/target-arm/helper-a64.c b/target-arm/helper-a64.c
index cccaac623076a16f7c90d1e9e91c9958d814ed0a..d3f706754fa1511c8d7a5f40318f9ec9015bc3f6 100644
--- a/target-arm/helper-a64.c
+++ b/target-arm/helper-a64.c
@@ -50,6 +50,16 @@ uint64_t HELPER(clz64)(uint64_t x)
     return clz64(x);
 }
 
+uint64_t HELPER(cls64)(uint64_t x)
+{
+    return clrsb64(x);
+}
+
+uint32_t HELPER(cls32)(uint32_t x)
+{
+    return clrsb32(x);
+}
+
 uint64_t HELPER(rbit64)(uint64_t x)
 {
     /* assign the correct byte position */
diff --git a/target-arm/helper-a64.h b/target-arm/helper-a64.h
index 9959139157e2100980025d2c8abf6e7a21f2ff00..a163a943222c369f84ce72fba2d6f7813b181f6b 100644
--- a/target-arm/helper-a64.h
+++ b/target-arm/helper-a64.h
@@ -19,4 +19,6 @@
 DEF_HELPER_FLAGS_2(udiv64, TCG_CALL_NO_RWG_SE, i64, i64, i64)
 DEF_HELPER_FLAGS_2(sdiv64, TCG_CALL_NO_RWG_SE, s64, s64, s64)
 DEF_HELPER_FLAGS_1(clz64, TCG_CALL_NO_RWG_SE, i64, i64)
+DEF_HELPER_FLAGS_1(cls64, TCG_CALL_NO_RWG_SE, i64, i64)
+DEF_HELPER_FLAGS_1(cls32, TCG_CALL_NO_RWG_SE, i32, i32)
 DEF_HELPER_FLAGS_1(rbit64, TCG_CALL_NO_RWG_SE, i64, i64)
diff --git a/target-arm/translate-a64.c b/target-arm/translate-a64.c
index 2111bcdd10279140a63b3de139057f641caefafd..2bb1795959e9411be671d657be6144043d4cedce 100644
--- a/target-arm/translate-a64.c
+++ b/target-arm/translate-a64.c
@@ -1114,6 +1114,24 @@ static void handle_clz(DisasContext *s, unsigned int sf,
     }
 }
 
+static void handle_cls(DisasContext *s, unsigned int sf,
+                       unsigned int rn, unsigned int rd)
+{
+    TCGv_i64 tcg_rd, tcg_rn;
+    tcg_rd = cpu_reg(s, rd);
+    tcg_rn = cpu_reg(s, rn);
+
+    if (sf) {
+        gen_helper_cls64(tcg_rd, tcg_rn);
+    } else {
+        TCGv_i32 tcg_tmp32 = tcg_temp_new_i32();
+        tcg_gen_trunc_i64_i32(tcg_tmp32, tcg_rn);
+        gen_helper_cls32(tcg_tmp32, tcg_tmp32);
+        tcg_gen_extu_i32_i64(tcg_rd, tcg_tmp32);
+        tcg_temp_free_i32(tcg_tmp32);
+    }
+}
+
 static void handle_rbit(DisasContext *s, unsigned int sf,
                         unsigned int rn, unsigned int rd)
 {
@@ -1236,7 +1254,7 @@ static void disas_data_proc_1src(DisasContext *s, uint32_t insn)
         handle_clz(s, sf, rn, rd);
         break;
     case 5: /* CLS */
-        unsupported_encoding(s, insn);
+        handle_cls(s, sf, rn, rd);
         break;
     }
 }