diff --git a/src/Nest/Analysis/TokenFilters/PatternReplaceTokenFilter.cs b/src/Nest/Analysis/TokenFilters/PatternReplaceTokenFilter.cs
index 3a6fe923705..098865984f9 100644
--- a/src/Nest/Analysis/TokenFilters/PatternReplaceTokenFilter.cs
+++ b/src/Nest/Analysis/TokenFilters/PatternReplaceTokenFilter.cs
@@ -7,6 +7,12 @@ namespace Nest
 	/// </summary>
 	public interface IPatternReplaceTokenFilter : ITokenFilter
 	{
+		/// <summary>
+		/// The flags for the regular expression
+		/// </summary>
+		[DataMember(Name ="flags")]
+		string Flags { get; set; }
+
 		/// <summary>
 		/// The regular expression
 		/// </summary>
@@ -25,6 +31,9 @@ public class PatternReplaceTokenFilter : TokenFilterBase, IPatternReplaceTokenFi
 	{
 		public PatternReplaceTokenFilter() : base("pattern_replace") { }
 
+		/// <inheritdoc />
+		public string Flags { get; set; }
+
 		/// <inheritdoc />
 		public string Pattern { get; set; }
 
@@ -39,13 +48,16 @@ public class PatternReplaceTokenFilterDescriptor
 		protected override string Type => "pattern_replace";
 
 		string IPatternReplaceTokenFilter.Pattern { get; set; }
-
 		string IPatternReplaceTokenFilter.Replacement { get; set; }
+		string IPatternReplaceTokenFilter.Flags { get; set; }
 
-		/// <inheritdoc />
+		/// <inheritdoc cref="IPatternReplaceTokenFilter.Flags" />
+		public PatternReplaceTokenFilterDescriptor Flags(string flags) => Assign(flags, (a, v) => a.Flags = v);
+
+		/// <inheritdoc cref="IPatternReplaceTokenFilter.Pattern" />
 		public PatternReplaceTokenFilterDescriptor Pattern(string pattern) => Assign(pattern, (a, v) => a.Pattern = v);
 
-		/// <inheritdoc />
+		/// <inheritdoc cref="IPatternReplaceTokenFilter.Replacement" />
 		public PatternReplaceTokenFilterDescriptor Replacement(string replacement) => Assign(replacement, (a, v) => a.Replacement = v);
 	}
 }
diff --git a/src/Tests/Tests/Analysis/TokenFilters/TokenFilterTests.cs b/src/Tests/Tests/Analysis/TokenFilters/TokenFilterTests.cs
index a79ba57bc4c..50483d07e13 100644
--- a/src/Tests/Tests/Analysis/TokenFilters/TokenFilterTests.cs
+++ b/src/Tests/Tests/Analysis/TokenFilters/TokenFilterTests.cs
@@ -347,7 +347,7 @@ public class MarkerTests : TokenFilterAssertionBase<MarkerTests>
 
 			public override string Name => "marker";
 		}
-		
+
 		public class MarkerWithPatternsTests : TokenFilterAssertionBase<MarkerWithPatternsTests>
 		{
 			public override FuncTokenFilters Fluent => (n, tf) => tf
@@ -493,16 +493,18 @@ public class PatternReplaceTests : TokenFilterAssertionBase<PatternReplaceTests>
 		{
 			public override FuncTokenFilters Fluent => (n, tf) => tf
 				.PatternReplace(n, t => t
+					.Flags("CASE_INSENSITIVE")
 					.Pattern(@"(\d|\w)")
 					.Replacement("replacement")
 				);
 
 			public override ITokenFilter Initializer =>
-				new PatternReplaceTokenFilter { Pattern = @"(\d|\w)", Replacement = "replacement" };
+				new PatternReplaceTokenFilter { Flags = "CASE_INSENSITIVE", Pattern = @"(\d|\w)", Replacement = "replacement" };
 
 			public override object Json => new
 			{
 				type = "pattern_replace",
+				flags = "CASE_INSENSITIVE",
 				pattern = "(\\d|\\w)",
 				replacement = "replacement"
 			};