diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
index 532a4a0..8da7a91 100644
--- a/target/s390x/cpu.h
+++ b/target/s390x/cpu.h
@@ -304,6 +304,7 @@ void s390x_cpu_debug_excp_handler(CPUState *cs);
 #undef PSW_MASK_WAIT
 #undef PSW_MASK_PSTATE
 #undef PSW_MASK_ASC
+#undef PSW_SHIFT_ASC
 #undef PSW_MASK_CC
 #undef PSW_MASK_PM
 #undef PSW_MASK_64
@@ -320,6 +321,7 @@ void s390x_cpu_debug_excp_handler(CPUState *cs);
 #define PSW_MASK_WAIT           0x0002000000000000ULL
 #define PSW_MASK_PSTATE         0x0001000000000000ULL
 #define PSW_MASK_ASC            0x0000C00000000000ULL
+#define PSW_SHIFT_ASC           46
 #define PSW_MASK_CC             0x0000300000000000ULL
 #define PSW_MASK_PM             0x00000F0000000000ULL
 #define PSW_MASK_64             0x0000000100000000ULL
@@ -353,15 +355,30 @@ void s390x_cpu_debug_excp_handler(CPUState *cs);
 #define FLAG_MASK_32            0x00001000
 
 /* Control register 0 bits */
+#define CR0_SECONDARY           0x0000002000000000ULL
 #define CR0_LOWPROT             0x0000000010000000ULL
 #define CR0_EDAT                0x0000000000800000ULL
 
+/* Control register 3 bits */
+#define CR3_PKM                 0x00000000ffff0000ULL
+
 /* MMU */
 #define MMU_PRIMARY_IDX         0
 #define MMU_SECONDARY_IDX       1
 #define MMU_HOME_IDX            2
 
-static inline int cpu_mmu_index (CPUS390XState *env, bool ifetch)
+static inline bool psw_key_valid(CPUS390XState *env, uint8_t psw_key)
+{
+    uint16_t pkm = ((env->cregs[3] & CR3_PKM) >> 16);
+
+    if (env->psw.mask & PSW_MASK_PSTATE) {
+        /* PSW key has range 0..15, it is valid if the bit is 1 in the PKM */
+        return pkm & (1 << (psw_key & 0xff));
+    }
+    return true;
+}
+
+static inline int cpu_mmu_index(CPUS390XState *env, bool ifetch)
 {
     switch (env->psw.mask & PSW_MASK_ASC) {
     case PSW_ASC_PRIMARY:
diff --git a/target/s390x/helper.c b/target/s390x/helper.c
index a468424..e5f4c6f 100644
--- a/target/s390x/helper.c
+++ b/target/s390x/helper.c
@@ -749,8 +749,8 @@ void s390x_cpu_debug_excp_handler(CPUState *cs)
 }
 
 /* Unaligned accesses are only diagnosed with MO_ALIGN.  At the moment,
-   this is only for the atomic operations, for which we want to raise a
-   specification exception.  */
+   this is only for operations, for which we want to raise a specification
+   exception.  */
 void s390x_cpu_do_unaligned_access(CPUState *cs, vaddr addr,
                                    MMUAccessType access_type,
                                    int mmu_idx, uintptr_t retaddr)
diff --git a/target/s390x/helper.h b/target/s390x/helper.h
index 69249a5..505f390 100644
--- a/target/s390x/helper.h
+++ b/target/s390x/helper.h
@@ -126,6 +126,7 @@ DEF_HELPER_FLAGS_2(tprot, TCG_CALL_NO_RWG, i32, i64, i64)
 DEF_HELPER_FLAGS_2(iske, TCG_CALL_NO_RWG_SE, i64, env, i64)
 DEF_HELPER_FLAGS_3(sske, TCG_CALL_NO_RWG, void, env, i64, i64)
 DEF_HELPER_FLAGS_2(rrbe, TCG_CALL_NO_RWG, i32, env, i64)
+DEF_HELPER_4(mvcos, i32, env, i64, i64, i64)
 DEF_HELPER_4(mvcs, i32, env, i64, i64, i64)
 DEF_HELPER_4(mvcp, i32, env, i64, i64, i64)
 DEF_HELPER_4(sigp, i32, env, i64, i32, i64)
diff --git a/target/s390x/insn-data.def b/target/s390x/insn-data.def
index d089707..6842de3 100644
--- a/target/s390x/insn-data.def
+++ b/target/s390x/insn-data.def
@@ -918,6 +918,8 @@
 /* LOAD USING REAL ADDRESS */
     C(0xb24b, LURA,    RRE,   Z,   0, r2, new, r1_32, lura, 0)
     C(0xb905, LURAG,   RRE,   Z,   0, r2, r1, 0, lurag, 0)
+/* MOVE WITH OPTIONAL SPECIFICATION */
+    C(0xc800, MVCOS,   SSF,   MVCOS, la1, a2, 0, 0, mvcos, 0)
 /* MOVE TO PRIMARY */
     C(0xda00, MVCP,    SS_d,  Z,   la1, a2, 0, 0, mvcp, 0)
 /* MOVE TO SECONDARY */
diff --git a/target/s390x/mem_helper.c b/target/s390x/mem_helper.c
index 80caab9..cb27465 100644
--- a/target/s390x/mem_helper.c
+++ b/target/s390x/mem_helper.c
@@ -1493,6 +1493,110 @@ uint32_t HELPER(rrbe)(CPUS390XState *env, uint64_t r2)
     return re >> 1;
 }
 
+uint32_t HELPER(mvcos)(CPUS390XState *env, uint64_t dest, uint64_t src,
+                       uint64_t len)
+{
+    const uint64_t r0 = env->regs[0];
+    const uint8_t psw_key = (env->psw.mask & PSW_MASK_KEY) >> PSW_SHIFT_KEY;
+    const uint8_t psw_as = (env->psw.mask & PSW_MASK_ASC) >> PSW_SHIFT_ASC;
+    const uintptr_t ra = GETPC();
+    uint8_t dest_key, dest_as, dest_k, dest_a;
+    uint8_t src_key, src_as, src_k, src_a;
+    uint64_t val;
+    int cc = 0, i;
+
+    HELPER_LOG("%s dest %" PRIx64 ", src %" PRIx64 ", len %" PRIx64 "\n",
+               __func__, dest, src, len);
+
+    if (!(env->psw.mask & PSW_MASK_DAT)) {
+        program_interrupt(env, PGM_SPECIAL_OP, 6);
+    }
+
+    /* OAC (operand access control) for the first operand -> dest */
+    val = (r0 & 0xffff0000ULL) >> 16;
+    dest_key = (val >> 12) & 0xf;
+    dest_as = (val >> 6) & 0x3;
+    dest_k = (val >> 1) & 0x1;
+    dest_a = (val) & 0x1;
+
+    /* OAC (operand access control) for the second operand -> src */
+    val = (r0 & 0x0000ffffULL);
+    src_key = (val >> 12) & 0xf;
+    src_as = (val >> 6) & 0x3;
+    src_k = (val >> 1) & 0x1;
+    src_a = (val) & 0x1;
+
+    if (!dest_k) {
+        dest_key = psw_key;
+    }
+    if (!src_k) {
+        src_key = psw_key;
+    }
+    if (!dest_a) {
+        dest_as = psw_as;
+    }
+    if (!src_a) {
+        src_as = psw_as;
+    }
+
+    if (dest_a && dest_as == 0x11 && (env->psw.mask & PSW_MASK_PSTATE)) {
+        program_interrupt(env, PGM_SPECIAL_OP, 6);
+    }
+    if (!(env->cregs[0] & CR0_SECONDARY) &&
+        (dest_as == 0x10 || src_as == 0x10)) {
+        program_interrupt(env, PGM_SPECIAL_OP, 6);
+    }
+    if (!psw_key_valid(env, dest_key) || !psw_key_valid(env, src_key)) {
+        program_interrupt(env, PGM_PRIVILEGED, 6);
+    }
+    /* FIXME: AR-mode and proper problem state mode (using PSW keys) missing */
+    if ((src_as | dest_as) == 0x01 || (env->psw.mask & PSW_MASK_PSTATE)) {
+        program_interrupt(env, PGM_ADDRESSING, 6);
+    }
+
+    if (len > 4096) {
+        cc = 3;
+        len = 4096;
+    }
+
+    /*
+     * FIXME: a) LAP protection
+     *        b) Access using correct PSW keys
+     *        c) AR-mode (mmu support missing)
+     *        d) bulk transfer
+     */
+    for (i = 0; i < len; i++, src++, dest++) {
+        uint8_t x = 0;
+
+        src = wrap_address(env, src);
+        dest = wrap_address(env, dest);
+        switch (src_as) {
+        case 0x0:
+            x = cpu_ldub_primary_ra(env, src, ra);
+            break;
+        case 0x2:
+            x = cpu_ldub_secondary_ra(env, src, ra);
+            break;
+        case 0x3:
+            x = cpu_ldub_home_ra(env, src, ra);
+            break;
+        }
+        switch (dest_as) {
+        case 0x0:
+            cpu_stb_primary_ra(env, dest, x, ra);
+            break;
+        case 0x2:
+            cpu_stb_secondary_ra(env, dest, x, ra);
+            break;
+        case 0x3:
+            cpu_stb_home_ra(env, dest, x, ra);
+            break;
+        }
+    }
+
+    return cc;
+}
+
 uint32_t HELPER(mvcs)(CPUS390XState *env, uint64_t l, uint64_t a1, uint64_t a2)
 {
     uintptr_t ra = GETPC();
diff --git a/target/s390x/translate.c b/target/s390x/translate.c
index fae006f..d1cc6c3 100644
--- a/target/s390x/translate.c
+++ b/target/s390x/translate.c
@@ -1202,6 +1202,7 @@ typedef enum DisasFacility {
     FAC_SCF,                /* store clock fast */
     FAC_SFLE,               /* store facility list extended */
     FAC_ILA,                /* interlocked access facility 1 */
+    FAC_MVCOS,              /* move-with-optional-specification */
     FAC_LPP,                /* load-program-parameter */
     FAC_DAT_ENH,            /* DAT-enhancement */
     FAC_E2,                 /* extended-translation facility 2 */
@@ -3069,6 +3070,15 @@ static ExitStatus op_mvclu(DisasContext *s, DisasOps *o)
 }
 
 #ifndef CONFIG_USER_ONLY
+static ExitStatus op_mvcos(DisasContext *s, DisasOps *o)
+{
+    int r3 = get_field(s->fields, r3);
+    potential_page_fault(s);
+    gen_helper_mvcos(cc_op, cpu_env, o->addr1, o->in2, regs[r3]);
+    set_cc_static(s);
+    return NO_EXIT;
+}
+
 static ExitStatus op_mvcp(DisasContext *s, DisasOps *o)
 {
     int r1 = get_field(s->fields, l1);
