diff --git a/wadsrc/static/zscript/base.txt b/wadsrc/static/zscript/base.txt
index 9defba9de..7fe034f0b 100644
--- a/wadsrc/static/zscript/base.txt
+++ b/wadsrc/static/zscript/base.txt
@@ -639,15 +639,15 @@ enum EPickStart
 // Although String is a builtin type, this is a convenient way to attach methods to it.
 struct StringStruct native
 {
-	native static vararg String Format(String fmt, ...);
+	native static vararg String Format(String fmt, ...) const;
 	native vararg void AppendFormat(String fmt, ...);
 
 	native void Replace(String pattern, String replacement);
-	native String Left(int len);
-	native String Mid(int pos = 0, int len = 2147483647);
+	native String Left(int len) const;
+	native String Mid(int pos = 0, int len = 2147483647) const;
 	native void Truncate(int newlen);
-	native String CharAt(int pos);
-	native int CharCodeAt(int pos);
+	native String CharAt(int pos) const;
+	native int CharCodeAt(int pos) const;
 	native String Filter();
 }