diff --git a/TextFilter.Test/TextFilterTests.cs b/TextFilter.Test/TextFilterTests.cs
index 66011f5..e61d8aa 100644
--- a/TextFilter.Test/TextFilterTests.cs
+++ b/TextFilter.Test/TextFilterTests.cs
@@ -682,6 +682,35 @@ public void ARegexCompiledUnderOneCultureAnswersTheSameUnderAnother()
 		}
 	}
 
+	[TestMethod]
+	public void AnInlineIgnoreCaseFoldsTheSameWhateverCultureCompiledIt()
+	{
+		// Under CaseSensitive the pattern can still ask for a fold itself with (?i), and that fold is
+		// culture-dependent unless CultureInvariant is set. Compiled under tr-TR first, "(?i)img" would
+		// then miss "IMG_1234.JPG" for every later caller, because the cache keeps the first compile.
+		CultureInfo original = CultureInfo.CurrentCulture;
+		try
+		{
+			CultureInfo.CurrentCulture = new CultureInfo("tr-TR");
+			if (CultureInfo.CurrentCulture.TextInfo.ToUpper("i") == "I")
+			{
+				Assert.Inconclusive("This runtime does not apply Turkish case mapping, so the regression cannot be provoked here.");
+			}
+
+			bool underTurkish = TextFilter.IsMatch("IMG_1234.JPG", "(?i)img", TextFilterType.Regex, TextFilterMatchOptions.ByWholeString);
+
+			CultureInfo.CurrentCulture = new CultureInfo("en-US");
+			bool underEnglish = TextFilter.IsMatch("IMG_1234.JPG", "(?i)img", TextFilterType.Regex, TextFilterMatchOptions.ByWholeString);
+
+			Assert.IsTrue(underTurkish, "An inline (?i) should fold i and I whatever locale compiled the pattern.");
+			Assert.IsTrue(underEnglish, "The first caller's culture should not decide the answer for later callers.");
+		}
+		finally
+		{
+			CultureInfo.CurrentCulture = original;
+		}
+	}
+
 	[TestMethod]
 	public void TheTwoSensitivitiesDoNotCollideInTheRegexCache()
 	{
diff --git a/TextFilter/TextFilter.cs b/TextFilter/TextFilter.cs
index 65c8a36..60af356 100644
--- a/TextFilter/TextFilter.cs
+++ b/TextFilter/TextFilter.cs
@@ -458,10 +458,12 @@ public static bool DoesMatchRegex(string text, string filter, TextFilterMatchOpt
 			// matches "IMG_1234.JPG" -- and the cache below is keyed by pattern and sensitivity only,
 			// so whichever culture happened to compile the pattern first decides the answer for every
 			// later caller on any thread. A filter pattern is machine text, not prose, and the glob
-			// path already folds invariantly, so the two paths now agree.
+			// path already folds invariantly, so the two paths now agree. It applies under CaseSensitive
+			// too, because the pattern itself can ask for a fold with an inline (?i), and that fold is
+			// just as culture-dependent and just as cached as the one the option asks for.
 			RegexOptions regexOptions = caseSensitivity is TextFilterCaseSensitivity.CaseInsensitive
 				? RegexOptions.Compiled | RegexOptions.IgnoreCase | RegexOptions.CultureInvariant
-				: RegexOptions.Compiled;
+				: RegexOptions.Compiled | RegexOptions.CultureInvariant;
 
 			try
 			{