diff --git a/src/test/java/picocli/Issue1904.java b/src/test/java/picocli/Issue1904.java
new file mode 100644
index 000000000..a7d6a005d
--- /dev/null
+++ b/src/test/java/picocli/Issue1904.java
@@ -0,0 +1,76 @@
+package picocli;
+
+import org.junit.Test;
+
+import java.io.File;
+import java.util.*;
+
+import static org.junit.Assert.*;
+
+public class Issue1904 {
+
+    enum DebugFacility { FOO, BAR, BAZ, ALL }
+
+    @CommandLine.Command
+    static class TestCommand implements Runnable {
+
+        @CommandLine.Option(
+            names = {"--debug"},
+            paramLabel = "FACILITY",
+            split = ",",
+            arity = "0..1",
+            fallbackValue = "ALL"
+        )
+        public Set<DebugFacility> debugFacilities = Collections.emptySet();
+
+        @CommandLine.Parameters(arity = "1..*")
+        public List<File> paths;
+
+        public void run() {}
+    }
+
+    @Test
+    public void singleOption() {
+        final CommandLine commandLine = new CommandLine(new TestCommand());
+        final CommandLine.ParseResult parseResult = commandLine.parseArgs("--debug", "ALL", "example.txt");
+        final TestCommand command = (TestCommand) parseResult.commandSpec().userObject();
+        assertEquals(EnumSet.of(DebugFacility.ALL), command.debugFacilities);
+        assertFalse(command.paths.isEmpty());
+    }
+
+    @Test
+    public void singleOptionWithCommandSeparatedValues() {
+        final CommandLine commandLine = new CommandLine(new TestCommand());
+        final CommandLine.ParseResult parseResult = commandLine.parseArgs("--debug", "FOO,BAR", "example.txt");
+        final TestCommand command = (TestCommand) parseResult.commandSpec().userObject();
+        assertEquals(EnumSet.of(DebugFacility.FOO, DebugFacility.BAR), command.debugFacilities);
+        assertFalse(command.paths.isEmpty());
+    }
+
+    @Test
+    public void singleOptionWithFallback() {
+        final CommandLine commandLine = new CommandLine(new TestCommand());
+        final CommandLine.ParseResult parseResult = commandLine.parseArgs("--debug", "example.txt");
+        final TestCommand command = (TestCommand) parseResult.commandSpec().userObject();
+        assertEquals(EnumSet.of(DebugFacility.ALL), command.debugFacilities);
+        assertFalse(command.paths.isEmpty());
+    }
+
+    @Test
+    public void multipleOptions() {
+        final CommandLine commandLine = new CommandLine(new TestCommand());
+        final CommandLine.ParseResult parseResult = commandLine.parseArgs("--debug", "FOO", "--debug", "BAR", "example.txt");
+        final TestCommand command = (TestCommand) parseResult.commandSpec().userObject();
+        assertEquals(EnumSet.of(DebugFacility.FOO, DebugFacility.BAR), command.debugFacilities);
+        assertFalse(command.paths.isEmpty());
+    }
+
+    @Test
+    public void multipleOptionsWithFallback() {
+        final CommandLine commandLine = new CommandLine(new TestCommand());
+        final CommandLine.ParseResult parseResult = commandLine.parseArgs("--debug", "--debug", "BAR", "example.txt");
+        final TestCommand command = (TestCommand) parseResult.commandSpec().userObject();
+        assertEquals(EnumSet.of(DebugFacility.ALL, DebugFacility.BAR), command.debugFacilities);
+        assertFalse(command.paths.isEmpty());
+    }
+}