diff --git a/tcg/tcg-op-ldst.c b/tcg/tcg-op-ldst.c
index e2c55df217..f11043b449 100644
--- a/tcg/tcg-op-ldst.c
+++ b/tcg/tcg-op-ldst.c
@@ -77,6 +77,13 @@ static MemOp tcg_canonicalize_memop(MemOp op, bool is64, bool st)
     if (st) {
         op &= ~MO_SIGN;
     }
+
+    /* In serial mode, reduce atomicity. */
+    if (!(tcg_ctx->gen_tb->cflags & CF_PARALLEL)) {
+        op &= ~MO_ATOM_MASK;
+        op |= MO_ATOM_NONE;
+    }
+
     return op;
 }
 
@@ -428,8 +435,7 @@ static bool use_two_i64_for_i128(MemOp mop)
     case MO_ATOM_SUBALIGN:
     case MO_ATOM_WITHIN16:
     case MO_ATOM_WITHIN16_PAIR:
-        /* In a serialized context, no atomicity is required. */
-        return !(tcg_ctx->gen_tb->cflags & CF_PARALLEL);
+        return false;
     default:
         g_assert_not_reached();
     }
@@ -499,13 +505,20 @@ static void maybe_free_addr64(TCGv_i64 a64)
 static void tcg_gen_qemu_ld_i128_int(TCGv_i128 val, TCGTemp *addr,
                                      TCGArg idx, MemOp memop)
 {
-    const MemOpIdx orig_oi = make_memop_idx(memop, idx);
+    MemOpIdx orig_oi;
     TCGv_i64 ext_addr = NULL;
     TCGOpcode opc;
 
     check_max_alignment(get_alignment_bits(memop));
     tcg_gen_req_mo(TCG_MO_LD_LD | TCG_MO_ST_LD);
 
+    /* In serial mode, reduce atomicity. */
+    if (!(tcg_ctx->gen_tb->cflags & CF_PARALLEL)) {
+        memop &= ~MO_ATOM_MASK;
+        memop |= MO_ATOM_NONE;
+    }
+    orig_oi = make_memop_idx(memop, idx);
+
     /* TODO: For now, force 32-bit hosts to use the helper. */
     if (TCG_TARGET_HAS_qemu_ldst_i128 && TCG_TARGET_REG_BITS == 64) {
         TCGv_i64 lo, hi;
@@ -608,13 +621,20 @@ void tcg_gen_qemu_ld_i128_chk(TCGv_i128 val, TCGTemp *addr, TCGArg idx,
 static void tcg_gen_qemu_st_i128_int(TCGv_i128 val, TCGTemp *addr,
                                      TCGArg idx, MemOp memop)
 {
-    const MemOpIdx orig_oi = make_memop_idx(memop, idx);
+    MemOpIdx orig_oi;
     TCGv_i64 ext_addr = NULL;
     TCGOpcode opc;
 
     check_max_alignment(get_alignment_bits(memop));
     tcg_gen_req_mo(TCG_MO_ST_LD | TCG_MO_ST_ST);
 
+    /* In serial mode, reduce atomicity. */
+    if (!(tcg_ctx->gen_tb->cflags & CF_PARALLEL)) {
+        memop &= ~MO_ATOM_MASK;
+        memop |= MO_ATOM_NONE;
+    }
+    orig_oi = make_memop_idx(memop, idx);
+
     /* TODO: For now, force 32-bit hosts to use the helper. */
 
     if (TCG_TARGET_HAS_qemu_ldst_i128 && TCG_TARGET_REG_BITS == 64) {
diff --git a/tcg/tcg.c b/tcg/tcg.c
index d2ea22b397..896a36caeb 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -5440,15 +5440,8 @@ static TCGAtomAlign atom_and_align_for_opc(TCGContext *s, MemOp opc,
     MemOp align = get_alignment_bits(opc);
     MemOp size = opc & MO_SIZE;
     MemOp half = size ? size - 1 : 0;
+    MemOp atom = opc & MO_ATOM_MASK;
     MemOp atmax;
-    MemOp atom;
-
-    /* When serialized, no further atomicity required.  */
-    if (s->gen_tb->cflags & CF_PARALLEL) {
-        atom = opc & MO_ATOM_MASK;
-    } else {
-        atom = MO_ATOM_NONE;
-    }
 
     switch (atom) {
     case MO_ATOM_NONE: