diff --git a/src/CommandLine/Core/Tokenizer.cs b/src/CommandLine/Core/Tokenizer.cs
index c588a98f..00314a7c 100644
--- a/src/CommandLine/Core/Tokenizer.cs
+++ b/src/CommandLine/Core/Tokenizer.cs
@@ -68,7 +68,7 @@ public static Result<IEnumerable<Token>, Error> ExplodeOptionList(
                         Tuple.Create(-1, '\0'))).SkipWhile(x => x.Item1 < 0).Memoize();
 
             var exploded = tokens.Select((t, i) =>
-                        replaces.FirstOrDefault(x => x.Item1 == i).ToMaybe()
+                        replaces.FirstOrDefault(x => x.Item1 == i && t.Tag == TokenType.Value).ToMaybe()
                             .MapValueOrDefault(r => t.Text.Split(r.Item2).Select(Token.Value),
                                 Enumerable.Empty<Token>().Concat(new[] { t })));
 
diff --git a/tests/CommandLine.Tests/Unit/Issue420Tests.cs b/tests/CommandLine.Tests/Unit/Issue420Tests.cs
new file mode 100644
index 00000000..cad06c46
--- /dev/null
+++ b/tests/CommandLine.Tests/Unit/Issue420Tests.cs
@@ -0,0 +1,50 @@
+using FluentAssertions;
+using System.Collections.Generic;
+using Xunit;
+
+namespace CommandLine.Tests.Unit
+{
+    public class Issue420Tests
+    {
+        // Test method (xUnit) which fails
+        [Fact]
+        public void parsing_of_enumerable_types_with_separator_chars_should_validate_value_is_present()
+        {
+            string[] args = { "-j", "1", "--categories", "--flag" };
+
+            ParserResult<Options> parsedOptions = Parser.Default.ParseArguments<Options>(args);
+
+            parsedOptions.Tag.Should().Be(ParserResultType.NotParsed);
+
+            ParserResult<OptionsWithSeparator> parsedOptionsWithSeparator = Parser.Default.ParseArguments<OptionsWithSeparator>(args);
+
+            parsedOptionsWithSeparator.Tag.Should().Be(ParserResultType.NotParsed);
+        }
+
+        // Options
+        internal class Options
+        {
+            [Option('f', "flag", HelpText = "Flag")]
+            public bool Flag { get; set; }
+
+            [Option('c', "categories", Required = false, HelpText = "Categories")]
+            public IEnumerable<string> Categories { get; set; }
+
+            [Option('j', "jobId", Required = true, HelpText = "Texts.ExplainJob")]
+            public int JobId { get; set; }
+        }
+
+        // Options
+        internal class OptionsWithSeparator
+        {
+            [Option('f', "flag", HelpText = "Flag")]
+            public bool Flag { get; set; }
+
+            [Option('c', "categories", Required = false, Separator = ',', HelpText = "Categories")]
+            public IEnumerable<string> Categories { get; set; }
+
+            [Option('j', "jobId", Required = true, HelpText = "Texts.ExplainJob")]
+            public int JobId { get; set; }
+        }
+    }
+}