diff --git a/include/fast_float/decimal_to_binary.h b/include/fast_float/decimal_to_binary.h
index a16d2c5..273f0b7 100644
--- a/include/fast_float/decimal_to_binary.h
+++ b/include/fast_float/decimal_to_binary.h
@@ -163,7 +163,8 @@ compute_float(int64_t q, uint64_t w) noexcept {
     // std::float16_t (e.g., 2^-25 = 298023223876953125e-25), so we apply the
     // same round-to-even test as in the normal case below.
     // See script/format_parameters.py.
-    if ((product.low <= 1) && (q >= binary::min_exponent_round_to_even()) &&
+    if (binary::subnormal_ties_possible() && (product.low <= 1) &&
+        (q >= binary::min_exponent_round_to_even()) &&
         (q <= binary::max_exponent_round_to_even()) &&
         ((answer.mantissa & 3) == 1)) {
       if (((answer.mantissa << subnormal_shift) << shift) == product.high) {
diff --git a/include/fast_float/float_common.h b/include/fast_float/float_common.h
index 77858da..76d94b3 100644
--- a/include/fast_float/float_common.h
+++ b/include/fast_float/float_common.h
@@ -225,12 +225,16 @@ using parse_options = parse_options_t<char>;
 
 #ifndef FASTFLOAT_ASSERT
 #define FASTFLOAT_ASSERT(x)                                                    \
-  { static_cast<void>(x); }
+  {                                                                            \
+    static_cast<void>(x);                                                      \
+  }
 #endif
 
 #ifndef FASTFLOAT_DEBUG_ASSERT
 #define FASTFLOAT_DEBUG_ASSERT(x)                                              \
-  { static_cast<void>(x); }
+  {                                                                            \
+    static_cast<void>(x);                                                      \
+  }
 #endif
 
 // rust style `try!()` macro, or `?` operator
@@ -662,6 +666,7 @@ template <typename T> struct binary_format : binary_format_lookup_tables<T> {
   static constexpr uint64_t
   max_mantissa_fast_path(); // used when fegetround() == FE_TONEAREST
   static constexpr bool fast_path_can_overflow();
+  static constexpr bool subnormal_ties_possible();
   static constexpr int largest_power_of_ten();
   static constexpr int smallest_power_of_ten();
   static constexpr T exact_power_of_ten(int64_t power);
@@ -1110,6 +1115,15 @@ inline constexpr bool binary_format<T>::fast_path_can_overflow() {
          double((std::numeric_limits<T>::max)());
 }
 
+// A subnormal needs w * 10^q < 2^(minimum_exponent() + 1), so q is at most
+// (minimum_exponent() + 1) * log10(2), with 1233/4096 < log10(2). Only
+// std::float16_t has such q in its round-to-even range.
+template <typename T>
+inline constexpr bool binary_format<T>::subnormal_ties_possible() {
+  return min_exponent_round_to_even() <=
+         (((minimum_exponent() + 1) * 1233) >> 12);
+}
+
 template <>
 inline constexpr uint64_t
 binary_format<double>::max_mantissa_fast_path(int64_t power) {
diff --git a/script/format_parameters.py b/script/format_parameters.py
index 1fb5cda..e981b8f 100644
--- a/script/format_parameters.py
+++ b/script/format_parameters.py
@@ -310,6 +310,11 @@ def check_ties(fmt):
         check(lo <= min(sub), "and the subnormal ties at q in [%d, %d]" % (min(sub), max(sub)))
     else:
         note("no subnormal tie has fewer than 20 digits")
+    # subnormal_ties_possible() in float_common.h: an upper bound on the
+    # largest q that can give a subnormal, compared with the tie range
+    q_sub = ((fmt.minimum_exponent + 1) * 1233) >> 12
+    check(10**q_sub < 2**fmt.emin < 10 ** (q_sub + 2), "q <= %d bounds the subnormal exponents" % q_sub)
+    check((lo <= q_sub) == bool(sub), "subnormal_ties_possible() == %s" % bool(sub))
     longest = len(str(((1 << (p + 2)) - 1) * 5**fmt.bias))
     check(fmt.max_digits >= longest, "max_digits=%d >= %d, the longest tie" % (fmt.max_digits, longest))