diff --git a/src/core/CCString.mli b/src/core/CCString.mli
index 0e5e7ba0..519c42a5 100644
--- a/src/core/CCString.mli
+++ b/src/core/CCString.mli
@@ -182,6 +182,14 @@ val take : int -> string -> string
 (** [take n s] keeps only the [n] first chars of [s].
     @since 0.17 *)
 
+val take_while : (char -> bool) -> string -> string
+(** [take_while p s] keeps only the longest prefix [t] of [s] such that every
+    character [c] in [t] satisfies [f c]. *)
+
+val rtake_while : (char -> bool) -> string -> string
+(** [rtake_while p s] keeps only the longest suffix [t] of [s] such that every
+    character [c] in [t] satisfies [f c]. *)
+
 val drop : int -> string -> string
 (** [drop n s] removes the [n] first chars of [s].
     @since 0.17 *)