diff --git a/src/ArduinoJson/Numbers/FloatTraits.hpp b/src/ArduinoJson/Numbers/FloatTraits.hpp
index 94529a9c..1c4559d8 100644
--- a/src/ArduinoJson/Numbers/FloatTraits.hpp
+++ b/src/ArduinoJson/Numbers/FloatTraits.hpp
@@ -12,6 +12,7 @@
 #include <ArduinoJson/Polyfills/math.hpp>
 #include <ArduinoJson/Polyfills/preprocessor.hpp>
 #include <ArduinoJson/Polyfills/static_array.hpp>
+#include <ArduinoJson/Polyfills/type_traits.hpp>
 
 namespace ARDUINOJSON_NAMESPACE {
 
@@ -116,11 +117,28 @@ struct FloatTraits<T, 8 /*64bits*/> {
     return forge(0x7FEFFFFF, 0xFFFFFFFF);
   }
 
-  static T highest_for(int64_t) {
+  template <typename TOut>
+  static
+      typename enable_if<is_integral<TOut>::value && sizeof(TOut) < sizeof(T),
+                         T>::type
+      highest_for() {
+    // This conversion is safe because the destination type is smaller
+    return highest();
+  }
+
+  template <typename TOut>
+  static typename enable_if<is_integral<TOut>::value &&
+                                is_signed<TOut>::value && sizeof(TOut) == 8,
+                            T>::type  // TOut == int64_t
+  highest_for() {
     return forge(0x43DFFFFF, 0xFFFFFFFF);  //  9.2233720368547748e+18
   }
 
-  static T highest_for(uint64_t) {
+  template <typename TOut>
+  static typename enable_if<is_integral<TOut>::value &&
+                                is_unsigned<TOut>::value && sizeof(TOut) == 8,
+                            T>::type  // TOut == uint64_t
+  highest_for() {
     return forge(0x43EFFFFF, 0xFFFFFFFF);  //  1.8446744073709549568e+19
   }
 
@@ -220,19 +238,44 @@ struct FloatTraits<T, 4 /*32bits*/> {
     return forge(0x7f7fffff);
   }
 
-  static T highest_for(int32_t) {
+  template <typename TOut>
+  static
+      typename enable_if<is_integral<TOut>::value && sizeof(TOut) < sizeof(T),
+                         T>::type
+      highest_for() {
+    // This conversion is safe because the destination type is smaller
+    return highest();
+  }
+
+  template <typename TOut>
+  static typename enable_if<is_integral<TOut>::value &&
+                                is_signed<TOut>::value && sizeof(TOut) == 4,
+                            T>::type  // TOut == int32_t
+  highest_for() {
     return forge(0x4EFFFFFF);  // 2.14748352E9
   }
 
-  static T highest_for(uint32_t) {
+  template <typename TOut>
+  static typename enable_if<is_integral<TOut>::value &&
+                                is_unsigned<TOut>::value && sizeof(TOut) == 4,
+                            T>::type  // TOut == uint32_t
+  highest_for() {
     return forge(0x4F7FFFFF);  // 4.29496704E9
   }
 
-  static T highest_for(int64_t) {
+  template <typename TOut>
+  static typename enable_if<is_integral<TOut>::value &&
+                                is_signed<TOut>::value && sizeof(TOut) == 8,
+                            T>::type  // TOut == int64_t
+  highest_for() {
     return forge(0x5EFFFFFF);  // 9.22337148709896192E18
   }
 
-  static T highest_for(uint64_t) {
+  template <typename TOut>
+  static typename enable_if<is_integral<TOut>::value &&
+                                is_unsigned<TOut>::value && sizeof(TOut) == 8,
+                            T>::type  // TOut == uint64_t
+  highest_for() {
     return forge(0x5F7FFFFF);  // 1.844674297419792384E19
   }
 
diff --git a/src/ArduinoJson/Numbers/convertNumber.hpp b/src/ArduinoJson/Numbers/convertNumber.hpp
index 52a3f677..9bf54e8d 100644
--- a/src/ArduinoJson/Numbers/convertNumber.hpp
+++ b/src/ArduinoJson/Numbers/convertNumber.hpp
@@ -96,33 +96,22 @@ canConvertNumber(TIn value) {
   return value <= TIn(numeric_limits<TOut>::highest());
 }
 
-// float32 -> int8
 // float32 -> int16
-// float64 -> int32
-template <typename TOut, typename TIn>
-typename enable_if<is_floating_point<TIn>::value && is_integral<TOut>::value &&
-                       sizeof(TOut) < sizeof(TIn),
-                   bool>::type
-canConvertNumber(TIn value) {
-  return value >= numeric_limits<TOut>::lowest() &&
-         value <= numeric_limits<TOut>::highest();
-}
-
 // float32 -> int32
-// float32 -> uint32
 // float32 -> int64
+// float32 -> int8
+// float32 -> uint32
 // float32 -> uint64
+// float64 -> int32
 // float64 -> int64
 // float64 -> uint64
 template <typename TOut, typename TIn>
-typename enable_if<is_floating_point<TIn>::value && is_integral<TOut>::value &&
-                       sizeof(TOut) >= sizeof(TIn),
+typename enable_if<is_floating_point<TIn>::value && is_integral<TOut>::value,
                    bool>::type
 canConvertNumber(TIn value) {
-  // Avoid error "9.22337e+18 is outside the range of representable values of
-  // type 'long'"
   return value >= numeric_limits<TOut>::lowest() &&
-         value <= FloatTraits<TIn>::highest_for(TOut());
+         value <= numeric_limits<TOut>::highest() &&
+         value <= FloatTraits<TIn>::template highest_for<TOut>();
 }
 
 template <typename TOut, typename TIn>