diff --git a/Sources/Splash/Grammar/SwiftGrammar.swift b/Sources/Splash/Grammar/SwiftGrammar.swift
index d98aba4..0a4a023 100644
--- a/Sources/Splash/Grammar/SwiftGrammar.swift
+++ b/Sources/Splash/Grammar/SwiftGrammar.swift
@@ -41,8 +41,8 @@ private extension SwiftGrammar {
         "extension", "let", "var", "func", "typealias",
         "init", "guard", "if", "else", "return", "get",
         "throw", "throws", "for", "in", "open", "weak",
-        "import", "mutating", "associatedtype", "case",
-        "switch", "static", "do", "try", "catch", "as",
+        "import", "mutating", "nonmutating", "associatedtype",
+        "case", "switch", "static", "do", "try", "catch", "as",
         "super", "self", "set", "true", "false", "nil",
         "override", "where", "_", "default", "break",
         "#selector", "required", "willSet", "didSet",
diff --git a/Tests/SplashTests/Tests/DeclarationTests.swift b/Tests/SplashTests/Tests/DeclarationTests.swift
index 97c015c..688f8e3 100644
--- a/Tests/SplashTests/Tests/DeclarationTests.swift
+++ b/Tests/SplashTests/Tests/DeclarationTests.swift
@@ -722,6 +722,34 @@ final class DeclarationTests: SyntaxHighlighterTestCase {
         ])
     }
 
+    func testNonMutatingFunction() {
+        let components = highlighter.highlight("""
+        struct MyStruct {
+            nonmutating func doNotChangeState() { }
+        }
+        """)
+
+        XCTAssertEqual(components, [
+            .token("struct", .keyword),
+            .whitespace(" "),
+            .plainText("MyStruct"),
+            .whitespace(" "),
+            .plainText("{"),
+            .whitespace("\n    "),
+            .token("nonmutating", .keyword),
+            .whitespace(" "),
+            .token("func", .keyword),
+            .whitespace(" "),
+            .plainText("doNotChangeState()"),
+            .whitespace(" "),
+            .plainText("{"),
+            .whitespace(" "),
+            .plainText("}"),
+            .whitespace("\n"),
+            .plainText("}")
+        ])
+    }
+
     func testIndirectEnumDeclaration() {
         let components = highlighter.highlight("""
         indirect enum Content {
@@ -793,6 +821,7 @@ extension DeclarationTests {
             ("testFunctionDeclarationWithNonEscapedKeywordAsName", testFunctionDeclarationWithNonEscapedKeywordAsName),
             ("testFunctionDeclarationWithEscapedKeywordAsName", testFunctionDeclarationWithEscapedKeywordAsName),
             ("testFunctionDeclarationWithPreProcessors", testFunctionDeclarationWithPreProcessors),
+            ("testNonMutatingFunction", testNonMutatingFunction),
             ("testIndirectEnumDeclaration", testIndirectEnumDeclaration)
         ]
     }