diff --git a/Cargo.toml b/Cargo.toml
index 8ef892a..f044dc2 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ad-hoc-iter"
-version = "0.2.1"
+version = "0.2.2"
 description = "Ad-hoc exact size owning iterator macro and other optional utils"
 repository = "https://git.flanchan.moe/flanchan/ad-hoc-iter"
 keywords = ["iterator", "macro", "iter"]
diff --git a/src/maybe.rs b/src/maybe.rs
index ce27d84..2e13001 100644
--- a/src/maybe.rs
+++ b/src/maybe.rs
@@ -134,7 +134,7 @@ where U: IntoIterator<Item = T>
 	    false
 	}
     }
-    /// Map the single value with this function
+    /// Map the many value with this function
     #[inline] pub fn map_many<F, A>(self, fun: F) -> MaybeMany<T, A>
     where F: FnOnce(U) -> A,
 	  A: IntoIterator<Item=T>
@@ -146,6 +146,16 @@ where U: IntoIterator<Item = T>
 	}
     }
     
+    /// Mutate the many value with this function.
+    #[inline] pub fn on_many<F, A>(&mut self, fun: F) -> Option<A>
+    where F: FnOnce(&mut U) -> A,
+    {
+	match self {
+	    Self::Many(ref mut m) => Some(fun(m)),
+	    _ => None
+	}
+    }
+    
     /// Map the single value with this function
     #[inline] fn map_one<F>(self, fun: F) -> MaybeMany<T,U>
     where F: FnOnce(T) -> T