diff --git a/include/fmt/format-inl.h b/include/fmt/format-inl.h
index 87663901..db539346 100644
--- a/include/fmt/format-inl.h
+++ b/include/fmt/format-inl.h
@@ -245,9 +245,11 @@ struct fp {
   template <typename Float> explicit FMT_CONSTEXPR fp(Float n) { assign(n); }
 
   template <typename Float>
-  using is_supported = bool_constant<sizeof(Float) == sizeof(uint32_t) ||
-                                     sizeof(Float) == 2 * sizeof(uint32_t) ||
-                                     std::numeric_limits<Float>::digits == 64>;
+  using is_supported =
+      bool_constant<sizeof(Float) == sizeof(uint32_t) ||
+                    sizeof(Float) == sizeof(uint64_t) ||
+                    (sizeof(Float) == sizeof(uint128_t) &&
+                     std::numeric_limits<Float>::digits == 64)>;
 
   // Assigns d to this and return true iff predecessor is closer than successor.
   template <typename Float, FMT_ENABLE_IF(is_supported<Float>::value)>