diff --git a/src/Verify.Tests/Naming/UseTextForParametersTests.cs b/src/Verify.Tests/Naming/UseTextForParametersTests.cs
new file mode 100644
index 000000000..ea128f98d
--- /dev/null
+++ b/src/Verify.Tests/Naming/UseTextForParametersTests.cs
@@ -0,0 +1,29 @@
+public class UseTextForParametersTests
+{
+    // The text is appended to the file name verbatim, so it has to be a valid file name.
+    // A `:` used to pass validation and then, on Windows, divert the received file into an
+    // NTFS alternate data stream, so no received file appeared at all.
+    [Theory]
+    [InlineData("ratio 16:9")]
+    [InlineData("a*b")]
+    [InlineData("a?b")]
+    [InlineData("a|b")]
+    // `#` is reserved for the indexed-target namespace
+    [InlineData("a#1")]
+    public void InvalidCharactersThrow(string text)
+    {
+        var settings = new VerifySettings();
+
+        var exception = Assert.Throws<ArgumentException>(() => settings.UseTextForParameters(text));
+        Assert.Contains("Invalid character for file name", exception.Message);
+    }
+
+    [Fact]
+    public void ValidTextIsAccepted()
+    {
+        var settings = new VerifySettings();
+        settings.UseTextForParameters("ratio 16-9");
+
+        Assert.Equal("ratio 16-9", settings.parametersText);
+    }
+}
diff --git a/src/Verify/Guards.cs b/src/Verify/Guards.cs
index 96cb8cbc3..d9a286e72 100644
--- a/src/Verify/Guards.cs
+++ b/src/Verify/Guards.cs
@@ -16,6 +16,18 @@ public static void BadFileName(string name, [CallerArgumentExpression("name")] s
         }
     }
 
+    public static void BadParametersText(string value, [CallerArgumentExpression(nameof(value))] string argumentName = "")
+    {
+        BadFileName(value, argumentName);
+
+        // `#` starts the indexed-target namespace, so a value containing one would make
+        // this case's files look like the targets of another case.
+        if (value.Contains('#'))
+        {
+            throw new ArgumentException($"Invalid character for file name. Value: {value}. Char:#", argumentName);
+        }
+    }
+
     static char[] invalidPathChars = Path
         .GetInvalidPathChars()
         .Concat(invalidFileChars.Except(['/', '\\', ':']))
diff --git a/src/Verify/VerifySettings.cs b/src/Verify/VerifySettings.cs
index 8eaae309a..dce16fc8b 100644
--- a/src/Verify/VerifySettings.cs
+++ b/src/Verify/VerifySettings.cs
@@ -156,7 +156,12 @@ public VerifySettings()
     /// </summary>
     public void UseTextForParameters(string parametersText)
     {
-        Guards.AgainstBadExtension(parametersText);
+        // The text goes into the file name verbatim, so it is validated as a file name,
+        // the same as UseFileName, UseTypeName and UseMethodName. The extension guard
+        // used to be applied here, which let `:`, `*`, `?`, `"`, `<`, `>` and `|` through
+        // to fail at write time, or on Windows silently divert the received file into an
+        // NTFS alternate data stream.
+        Guards.BadParametersText(parametersText);
 
         if (parameters is not null)
         {