diff --git a/CHANGELOG.md b/CHANGELOG.md
index cd67e2f4..1f8062be 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ HEAD
 * Added support for `std::string_view` (issue #1578, PR #1554 by @0xFEEDC0DE64)
 * Fixed warning `definition of implicit copy constructor for 'MsgPackDeserializer' is deprecated because it has a user-declared copy assignment operator`
 * Added `JsonArray::clear()` (issue #1597)
+* Fixed `JsonVariant::as<unsigned>()` (issue #1601)
 
 v6.18.0 (2021-05-05)
 -------
diff --git a/extras/tests/JsonVariant/as.cpp b/extras/tests/JsonVariant/as.cpp
index 843f17dd..add6b10c 100644
--- a/extras/tests/JsonVariant/as.cpp
+++ b/extras/tests/JsonVariant/as.cpp
@@ -61,6 +61,16 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<std::string>() == "true");
   }
 
+  SECTION("set(42)") {
+    variant.set(42);
+
+    REQUIRE(variant.as<bool>() == true);
+    REQUIRE(variant.as<double>() == 42.0);
+    REQUIRE(variant.as<int>() == 42);
+    REQUIRE(variant.as<unsigned int>() == 42U);  // issue #1601
+    REQUIRE(variant.as<std::string>() == "42");
+  }
+
   SECTION("set(42L)") {
     variant.set(42L);
 
diff --git a/extras/tests/Numbers/CMakeLists.txt b/extras/tests/Numbers/CMakeLists.txt
index 7e799a3a..7d11034f 100644
--- a/extras/tests/Numbers/CMakeLists.txt
+++ b/extras/tests/Numbers/CMakeLists.txt
@@ -3,6 +3,7 @@
 # MIT License
 
 add_executable(NumbersTests 
+	convertNumber.cpp
 	parseFloat.cpp
 	parseDouble.cpp
 	parseInteger.cpp
diff --git a/extras/tests/Numbers/convertNumber.cpp b/extras/tests/Numbers/convertNumber.cpp
new file mode 100644
index 00000000..0fdc20db
--- /dev/null
+++ b/extras/tests/Numbers/convertNumber.cpp
@@ -0,0 +1,78 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright Benoit Blanchon 2014-2021
+// MIT License
+
+#include <stdint.h>
+#include <ArduinoJson.hpp>
+#include <catch.hpp>
+
+using namespace ARDUINOJSON_NAMESPACE;
+
+TEST_CASE("canConvertNumber<TOut, TIn>()") {
+  SECTION("int8_t -> int8_t") {
+    CHECK((canConvertNumber<int8_t, int8_t>(0)) == true);
+    CHECK((canConvertNumber<int8_t, int8_t>(127)) == true);
+    CHECK((canConvertNumber<int8_t, int8_t>(-128)) == true);
+  }
+
+  SECTION("int8_t -> int16_t") {
+    CHECK((canConvertNumber<int16_t, int8_t>(0)) == true);
+    CHECK((canConvertNumber<int16_t, int8_t>(127)) == true);
+    CHECK((canConvertNumber<int16_t, int8_t>(-128)) == true);
+  }
+
+  SECTION("int8_t -> uint8_t") {
+    CHECK((canConvertNumber<uint8_t, int8_t>(0)) == true);
+    CHECK((canConvertNumber<uint8_t, int8_t>(127)) == true);
+    CHECK((canConvertNumber<uint8_t, int8_t>(-128)) == false);
+  }
+
+  SECTION("int8_t -> uint16_t") {
+    CHECK((canConvertNumber<uint16_t, int8_t>(0)) == true);
+    CHECK((canConvertNumber<uint16_t, int8_t>(127)) == true);
+    CHECK((canConvertNumber<uint16_t, int8_t>(-128)) == false);
+  }
+
+  SECTION("int16_t -> int8_t") {
+    CHECK((canConvertNumber<int8_t, int16_t>(0)) == true);
+    CHECK((canConvertNumber<int8_t, int16_t>(127)) == true);
+    CHECK((canConvertNumber<int8_t, int16_t>(128)) == false);
+    CHECK((canConvertNumber<int8_t, int16_t>(-128)) == true);
+    CHECK((canConvertNumber<int8_t, int16_t>(-129)) == false);
+  }
+
+  SECTION("int16_t -> uint8_t") {
+    CHECK((canConvertNumber<uint8_t, int16_t>(0)) == true);
+    CHECK((canConvertNumber<uint8_t, int16_t>(255)) == true);
+    CHECK((canConvertNumber<uint8_t, int16_t>(256)) == false);
+    CHECK((canConvertNumber<uint8_t, int16_t>(-1)) == false);
+  }
+
+  SECTION("uint8_t -> int8_t") {
+    CHECK((canConvertNumber<int8_t, uint8_t>(0)) == true);
+    CHECK((canConvertNumber<int8_t, uint8_t>(127)) == true);
+    CHECK((canConvertNumber<int8_t, uint8_t>(128)) == false);
+    CHECK((canConvertNumber<int8_t, uint8_t>(255)) == false);
+  }
+
+  SECTION("uint8_t -> int16_t") {
+    CHECK((canConvertNumber<int16_t, uint8_t>(0)) == true);
+    CHECK((canConvertNumber<int16_t, uint8_t>(127)) == true);
+    CHECK((canConvertNumber<int16_t, uint8_t>(128)) == true);
+    CHECK((canConvertNumber<int16_t, uint8_t>(255)) == true);
+  }
+
+  SECTION("uint8_t -> uint8_t") {
+    CHECK((canConvertNumber<uint8_t, uint8_t>(0)) == true);
+    CHECK((canConvertNumber<uint8_t, uint8_t>(127)) == true);
+    CHECK((canConvertNumber<uint8_t, uint8_t>(128)) == true);
+    CHECK((canConvertNumber<uint8_t, uint8_t>(255)) == true);
+  }
+
+  SECTION("uint8_t -> uint16_t") {
+    CHECK((canConvertNumber<uint16_t, uint8_t>(0)) == true);
+    CHECK((canConvertNumber<uint16_t, uint8_t>(127)) == true);
+    CHECK((canConvertNumber<uint16_t, uint8_t>(128)) == true);
+    CHECK((canConvertNumber<uint16_t, uint8_t>(255)) == true);
+  }
+}
diff --git a/src/ArduinoJson/Numbers/convertNumber.hpp b/src/ArduinoJson/Numbers/convertNumber.hpp
index 8f2cd592..3087459f 100644
--- a/src/ArduinoJson/Numbers/convertNumber.hpp
+++ b/src/ArduinoJson/Numbers/convertNumber.hpp
@@ -71,9 +71,23 @@ canConvertNumber(TIn) {
 }
 
 // int32 -> uint32
+// int32 -> uint64
 template <typename TOut, typename TIn>
 typename enable_if<is_integral<TIn>::value && is_signed<TIn>::value &&
-                       is_integral<TOut>::value && is_unsigned<TOut>::value,
+                       is_integral<TOut>::value && is_unsigned<TOut>::value &&
+                       sizeof(TOut) >= sizeof(TIn),
+                   bool>::type
+canConvertNumber(TIn value) {
+  if (value < 0)
+    return false;
+  return TOut(value) <= numeric_limits<TOut>::highest();
+}
+
+// int32 -> uint16
+template <typename TOut, typename TIn>
+typename enable_if<is_integral<TIn>::value && is_signed<TIn>::value &&
+                       is_integral<TOut>::value && is_unsigned<TOut>::value &&
+                       sizeof(TOut) < sizeof(TIn),
                    bool>::type
 canConvertNumber(TIn value) {
   if (value < 0)