diff --git a/target/riscv/insn_trans/trans_rvf.inc.c b/target/riscv/insn_trans/trans_rvf.inc.c
index 264d3139f1..832f01db6f 100644
--- a/target/riscv/insn_trans/trans_rvf.inc.c
+++ b/target/riscv/insn_trans/trans_rvf.inc.c
@@ -161,47 +161,86 @@ static bool trans_fsgnj_s(DisasContext *ctx, arg_fsgnj_s *a)
 {
     REQUIRE_FPU;
     REQUIRE_EXT(ctx, RVF);
+
     if (a->rs1 == a->rs2) { /* FMOV */
-        tcg_gen_mov_i64(cpu_fpr[a->rd], cpu_fpr[a->rs1]);
+        gen_check_nanbox_s(cpu_fpr[a->rd], cpu_fpr[a->rs1]);
     } else { /* FSGNJ */
-        tcg_gen_deposit_i64(cpu_fpr[a->rd], cpu_fpr[a->rs2], cpu_fpr[a->rs1],
-                            0, 31);
+        TCGv_i64 rs1 = tcg_temp_new_i64();
+        TCGv_i64 rs2 = tcg_temp_new_i64();
+
+        gen_check_nanbox_s(rs1, cpu_fpr[a->rs1]);
+        gen_check_nanbox_s(rs2, cpu_fpr[a->rs2]);
+
+        /* This formulation retains the nanboxing of rs2. */
+        tcg_gen_deposit_i64(cpu_fpr[a->rd], rs2, rs1, 0, 31);
+        tcg_temp_free_i64(rs1);
+        tcg_temp_free_i64(rs2);
     }
-    gen_nanbox_s(cpu_fpr[a->rd], cpu_fpr[a->rd]);
     mark_fs_dirty(ctx);
     return true;
 }
 
 static bool trans_fsgnjn_s(DisasContext *ctx, arg_fsgnjn_s *a)
 {
+    TCGv_i64 rs1, rs2, mask;
+
     REQUIRE_FPU;
     REQUIRE_EXT(ctx, RVF);
+
+    rs1 = tcg_temp_new_i64();
+    gen_check_nanbox_s(rs1, cpu_fpr[a->rs1]);
+
     if (a->rs1 == a->rs2) { /* FNEG */
-        tcg_gen_xori_i64(cpu_fpr[a->rd], cpu_fpr[a->rs1], INT32_MIN);
+        tcg_gen_xori_i64(cpu_fpr[a->rd], rs1, MAKE_64BIT_MASK(31, 1));
     } else {
-        TCGv_i64 t0 = tcg_temp_new_i64();
-        tcg_gen_not_i64(t0, cpu_fpr[a->rs2]);
-        tcg_gen_deposit_i64(cpu_fpr[a->rd], t0, cpu_fpr[a->rs1], 0, 31);
-        tcg_temp_free_i64(t0);
+        rs2 = tcg_temp_new_i64();
+        gen_check_nanbox_s(rs2, cpu_fpr[a->rs2]);
+
+        /*
+         * Replace bit 31 in rs1 with inverse in rs2.
+         * This formulation retains the nanboxing of rs1.
+         */
+        mask = tcg_const_i64(~MAKE_64BIT_MASK(31, 1));
+        tcg_gen_nor_i64(rs2, rs2, mask);
+        tcg_gen_and_i64(rs1, mask, rs1);
+        tcg_gen_or_i64(cpu_fpr[a->rd], rs1, rs2);
+
+        tcg_temp_free_i64(mask);
+        tcg_temp_free_i64(rs2);
     }
-    gen_nanbox_s(cpu_fpr[a->rd], cpu_fpr[a->rd]);
+    tcg_temp_free_i64(rs1);
+
     mark_fs_dirty(ctx);
     return true;
 }
 
 static bool trans_fsgnjx_s(DisasContext *ctx, arg_fsgnjx_s *a)
 {
+    TCGv_i64 rs1, rs2;
+
     REQUIRE_FPU;
     REQUIRE_EXT(ctx, RVF);
+
+    rs1 = tcg_temp_new_i64();
+    gen_check_nanbox_s(rs1, cpu_fpr[a->rs1]);
+
     if (a->rs1 == a->rs2) { /* FABS */
-        tcg_gen_andi_i64(cpu_fpr[a->rd], cpu_fpr[a->rs1], ~INT32_MIN);
+        tcg_gen_andi_i64(cpu_fpr[a->rd], rs1, ~MAKE_64BIT_MASK(31, 1));
     } else {
-        TCGv_i64 t0 = tcg_temp_new_i64();
-        tcg_gen_andi_i64(t0, cpu_fpr[a->rs2], INT32_MIN);
-        tcg_gen_xor_i64(cpu_fpr[a->rd], cpu_fpr[a->rs1], t0);
-        tcg_temp_free_i64(t0);
+        rs2 = tcg_temp_new_i64();
+        gen_check_nanbox_s(rs2, cpu_fpr[a->rs2]);
+
+        /*
+         * Xor bit 31 in rs1 with that in rs2.
+         * This formulation retains the nanboxing of rs1.
+         */
+        tcg_gen_andi_i64(rs2, rs2, MAKE_64BIT_MASK(31, 1));
+        tcg_gen_xor_i64(cpu_fpr[a->rd], rs1, rs2);
+
+        tcg_temp_free_i64(rs2);
     }
-    gen_nanbox_s(cpu_fpr[a->rd], cpu_fpr[a->rd]);
+    tcg_temp_free_i64(rs1);
+
     mark_fs_dirty(ctx);
     return true;
 }
diff --git a/target/riscv/translate.c b/target/riscv/translate.c
index 12a746da97..bf35182776 100644
--- a/target/riscv/translate.c
+++ b/target/riscv/translate.c
@@ -101,6 +101,24 @@ static void gen_nanbox_s(TCGv_i64 out, TCGv_i64 in)
     tcg_gen_ori_i64(out, in, MAKE_64BIT_MASK(32, 32));
 }
 
+/*
+ * A narrow n-bit operation, where n < FLEN, checks that input operands
+ * are correctly Nan-boxed, i.e., all upper FLEN - n bits are 1.
+ * If so, the least-significant bits of the input are used, otherwise the
+ * input value is treated as an n-bit canonical NaN (v2.2 section 9.2).
+ *
+ * Here, the result is always nan-boxed, even the canonical nan.
+ */
+static void gen_check_nanbox_s(TCGv_i64 out, TCGv_i64 in)
+{
+    TCGv_i64 t_max = tcg_const_i64(0xffffffff00000000ull);
+    TCGv_i64 t_nan = tcg_const_i64(0xffffffff7fc00000ull);
+
+    tcg_gen_movcond_i64(TCG_COND_GEU, out, in, t_max, in, t_nan);
+    tcg_temp_free_i64(t_max);
+    tcg_temp_free_i64(t_nan);
+}
+
 static void generate_exception(DisasContext *ctx, int excp)
 {
     tcg_gen_movi_tl(cpu_pc, ctx->base.pc_next);
