diff --git a/Test/Flurl.Test/UrlBuilder/UrlBuildingTests.cs b/Test/Flurl.Test/UrlBuilder/UrlBuildingTests.cs
index 9f890ac..fbc12f2 100644
--- a/Test/Flurl.Test/UrlBuilder/UrlBuildingTests.cs
+++ b/Test/Flurl.Test/UrlBuilder/UrlBuildingTests.cs
@@ -302,6 +302,13 @@ namespace Flurl.Test.UrlBuilder
 			Assert.AreEqual("http://www.mysite.com?x=%2450&y=2%2B2%3D4", url.ToString());
 		}
 
+		[Test] // #582
+		public void encodes_date_type_query_param() {
+			var date = new DateTime(2020, 12, 6, 10, 45, 1);
+			var url = "http://www.mysite.com".SetQueryParam("date", date);
+			Assert.AreEqual("http://www.mysite.com?date=2020-12-06T10%3A45%3A01.0000000", url.ToString());
+		}
+
 		[Test]
 		public void does_not_reencode_encoded_query_values() {
 			var url = "http://www.mysite.com".SetQueryParam("x", "%CD%EE%E2%FB%E9%20%E3%EE%E4", true);
diff --git a/src/Flurl/QueryParamCollection.cs b/src/Flurl/QueryParamCollection.cs
index 93efeb7..6321d45 100644
--- a/src/Flurl/QueryParamCollection.cs
+++ b/src/Flurl/QueryParamCollection.cs
@@ -190,6 +190,6 @@ namespace Flurl
 			(Value == null) ? null :
 			(_encodedValue != null) ? _encodedValue :
 			(Value is string s) ? Url.Encode(s, encodeSpaceAsPlus) :
-			Value.ToInvariantString();
+			Url.Encode(Value.ToInvariantString(), encodeSpaceAsPlus);
 	}
 }
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