diff --git a/target/riscv/internals.h b/target/riscv/internals.h
index 9f4ba7d617..f1a546dba6 100644
--- a/target/riscv/internals.h
+++ b/target/riscv/internals.h
@@ -43,4 +43,15 @@ static inline uint64_t nanbox_s(float32 f)
     return f | MAKE_64BIT_MASK(32, 32);
 }
 
+static inline float32 check_nanbox_s(uint64_t f)
+{
+    uint64_t mask = MAKE_64BIT_MASK(32, 32);
+
+    if (likely((f & mask) == mask)) {
+        return (uint32_t)f;
+    } else {
+        return 0x7fc00000u; /* default qnan */
+    }
+}
+
 #endif
diff --git a/target/riscv/fpu_helper.c b/target/riscv/fpu_helper.c
index 72541958a7..bb346a8249 100644
--- a/target/riscv/fpu_helper.c
+++ b/target/riscv/fpu_helper.c
@@ -81,9 +81,12 @@ void helper_set_rounding_mode(CPURISCVState *env, uint32_t rm)
     set_float_rounding_mode(softrm, &env->fp_status);
 }
 
-static uint64_t do_fmadd_s(CPURISCVState *env, uint64_t frs1, uint64_t frs2,
-                           uint64_t frs3, int flags)
+static uint64_t do_fmadd_s(CPURISCVState *env, uint64_t rs1, uint64_t rs2,
+                           uint64_t rs3, int flags)
 {
+    float32 frs1 = check_nanbox_s(rs1);
+    float32 frs2 = check_nanbox_s(rs2);
+    float32 frs3 = check_nanbox_s(rs3);
     return nanbox_s(float32_muladd(frs1, frs2, frs3, flags, &env->fp_status));
 }
 
@@ -139,74 +142,97 @@ uint64_t helper_fnmadd_d(CPURISCVState *env, uint64_t frs1, uint64_t frs2,
                           float_muladd_negate_product, &env->fp_status);
 }
 
-uint64_t helper_fadd_s(CPURISCVState *env, uint64_t frs1, uint64_t frs2)
+uint64_t helper_fadd_s(CPURISCVState *env, uint64_t rs1, uint64_t rs2)
 {
+    float32 frs1 = check_nanbox_s(rs1);
+    float32 frs2 = check_nanbox_s(rs2);
     return nanbox_s(float32_add(frs1, frs2, &env->fp_status));
 }
 
-uint64_t helper_fsub_s(CPURISCVState *env, uint64_t frs1, uint64_t frs2)
+uint64_t helper_fsub_s(CPURISCVState *env, uint64_t rs1, uint64_t rs2)
 {
+    float32 frs1 = check_nanbox_s(rs1);
+    float32 frs2 = check_nanbox_s(rs2);
     return nanbox_s(float32_sub(frs1, frs2, &env->fp_status));
 }
 
-uint64_t helper_fmul_s(CPURISCVState *env, uint64_t frs1, uint64_t frs2)
+uint64_t helper_fmul_s(CPURISCVState *env, uint64_t rs1, uint64_t rs2)
 {
+    float32 frs1 = check_nanbox_s(rs1);
+    float32 frs2 = check_nanbox_s(rs2);
     return nanbox_s(float32_mul(frs1, frs2, &env->fp_status));
 }
 
-uint64_t helper_fdiv_s(CPURISCVState *env, uint64_t frs1, uint64_t frs2)
+uint64_t helper_fdiv_s(CPURISCVState *env, uint64_t rs1, uint64_t rs2)
 {
+    float32 frs1 = check_nanbox_s(rs1);
+    float32 frs2 = check_nanbox_s(rs2);
     return nanbox_s(float32_div(frs1, frs2, &env->fp_status));
 }
 
-uint64_t helper_fmin_s(CPURISCVState *env, uint64_t frs1, uint64_t frs2)
+uint64_t helper_fmin_s(CPURISCVState *env, uint64_t rs1, uint64_t rs2)
 {
+    float32 frs1 = check_nanbox_s(rs1);
+    float32 frs2 = check_nanbox_s(rs2);
     return nanbox_s(float32_minnum(frs1, frs2, &env->fp_status));
 }
 
-uint64_t helper_fmax_s(CPURISCVState *env, uint64_t frs1, uint64_t frs2)
+uint64_t helper_fmax_s(CPURISCVState *env, uint64_t rs1, uint64_t rs2)
 {
+    float32 frs1 = check_nanbox_s(rs1);
+    float32 frs2 = check_nanbox_s(rs2);
     return nanbox_s(float32_maxnum(frs1, frs2, &env->fp_status));
 }
 
-uint64_t helper_fsqrt_s(CPURISCVState *env, uint64_t frs1)
+uint64_t helper_fsqrt_s(CPURISCVState *env, uint64_t rs1)
 {
+    float32 frs1 = check_nanbox_s(rs1);
     return nanbox_s(float32_sqrt(frs1, &env->fp_status));
 }
 
-target_ulong helper_fle_s(CPURISCVState *env, uint64_t frs1, uint64_t frs2)
+target_ulong helper_fle_s(CPURISCVState *env, uint64_t rs1, uint64_t rs2)
 {
+    float32 frs1 = check_nanbox_s(rs1);
+    float32 frs2 = check_nanbox_s(rs2);
     return float32_le(frs1, frs2, &env->fp_status);
 }
 
-target_ulong helper_flt_s(CPURISCVState *env, uint64_t frs1, uint64_t frs2)
+target_ulong helper_flt_s(CPURISCVState *env, uint64_t rs1, uint64_t rs2)
 {
+    float32 frs1 = check_nanbox_s(rs1);
+    float32 frs2 = check_nanbox_s(rs2);
     return float32_lt(frs1, frs2, &env->fp_status);
 }
 
-target_ulong helper_feq_s(CPURISCVState *env, uint64_t frs1, uint64_t frs2)
+target_ulong helper_feq_s(CPURISCVState *env, uint64_t rs1, uint64_t rs2)
 {
+    float32 frs1 = check_nanbox_s(rs1);
+    float32 frs2 = check_nanbox_s(rs2);
     return float32_eq_quiet(frs1, frs2, &env->fp_status);
 }
 
-target_ulong helper_fcvt_w_s(CPURISCVState *env, uint64_t frs1)
+target_ulong helper_fcvt_w_s(CPURISCVState *env, uint64_t rs1)
 {
+    float32 frs1 = check_nanbox_s(rs1);
     return float32_to_int32(frs1, &env->fp_status);
 }
 
-target_ulong helper_fcvt_wu_s(CPURISCVState *env, uint64_t frs1)
+target_ulong helper_fcvt_wu_s(CPURISCVState *env, uint64_t rs1)
 {
+    float32 frs1 = check_nanbox_s(rs1);
     return (int32_t)float32_to_uint32(frs1, &env->fp_status);
 }
 
 #if defined(TARGET_RISCV64)
-uint64_t helper_fcvt_l_s(CPURISCVState *env, uint64_t frs1)
+uint64_t helper_fcvt_l_s(CPURISCVState *env, uint64_t rs1)
 {
+    float32 frs1 = check_nanbox_s(rs1);
     return float32_to_int64(frs1, &env->fp_status);
 }
 
-uint64_t helper_fcvt_lu_s(CPURISCVState *env, uint64_t frs1)
+uint64_t helper_fcvt_lu_s(CPURISCVState *env, uint64_t rs1)
 {
+    float32 frs1 = check_nanbox_s(rs1);
     return float32_to_uint64(frs1, &env->fp_status);
 }
 #endif
@@ -233,8 +259,9 @@ uint64_t helper_fcvt_s_lu(CPURISCVState *env, uint64_t rs1)
 }
 #endif
 
-target_ulong helper_fclass_s(uint64_t frs1)
+target_ulong helper_fclass_s(uint64_t rs1)
 {
+    float32 frs1 = check_nanbox_s(rs1);
     return fclass_s(frs1);
 }
 
@@ -275,7 +302,8 @@ uint64_t helper_fcvt_s_d(CPURISCVState *env, uint64_t rs1)
 
 uint64_t helper_fcvt_d_s(CPURISCVState *env, uint64_t rs1)
 {
-    return float32_to_float64(rs1, &env->fp_status);
+    float32 frs1 = check_nanbox_s(rs1);
+    return float32_to_float64(frs1, &env->fp_status);
 }
 
 uint64_t helper_fsqrt_d(CPURISCVState *env, uint64_t frs1)
