diff --git a/runtime/Swift/Sources/Antlr4/ANTLRFileStream.swift b/runtime/Swift/Sources/Antlr4/ANTLRFileStream.swift
index 3d75ac8ea7..ca66a8b362 100644
--- a/runtime/Swift/Sources/Antlr4/ANTLRFileStream.swift
+++ b/runtime/Swift/Sources/Antlr4/ANTLRFileStream.swift
@@ -13,10 +13,9 @@ public class ANTLRFileStream: ANTLRInputStream {
 
     public init(_ fileName: String, _ encoding: String.Encoding? = nil) throws {
         self.fileName = fileName
-        super.init()
         let fileContents = try String(contentsOfFile: fileName, encoding: encoding ?? .utf8)
-        data = fileContents.unicodeScalars
-        n = data.count
+        let unicodeScalars = fileContents.unicodeScalars
+        super.init(unicodeScalars, unicodeScalars.count)
     }
 
     override
diff --git a/runtime/Swift/Sources/Antlr4/ANTLRInputStream.swift b/runtime/Swift/Sources/Antlr4/ANTLRInputStream.swift
index 4f58641558..0f13fd534a 100644
--- a/runtime/Swift/Sources/Antlr4/ANTLRInputStream.swift
+++ b/runtime/Swift/Sources/Antlr4/ANTLRInputStream.swift
@@ -15,7 +15,7 @@ public class ANTLRInputStream: CharStream {
     ///
     /// The data being scanned
     /// 
-    internal var data: String.UnicodeScalarView
+    internal let data: String.UnicodeScalarView
 
     /// 
     /// How many unicode scalars are actually in the buffer