diff --git a/.changelog/unreleased/bug-fixes/863-immut-ref-in-validate.md b/.changelog/unreleased/bug-fixes/863-immut-ref-in-validate.md
new file mode 100644
index 000000000..91cbda02b
--- /dev/null
+++ b/.changelog/unreleased/bug-fixes/863-immut-ref-in-validate.md
@@ -0,0 +1,2 @@
+- Replace mutable ref with immutable ref in validate handler
+  ([\#863](https://github.com/cosmos/ibc-rs/issues/863))
\ No newline at end of file
diff --git a/crates/ibc/src/core/handler.rs b/crates/ibc/src/core/handler.rs
index 5ddebcf97..7c2babfe3 100644
--- a/crates/ibc/src/core/handler.rs
+++ b/crates/ibc/src/core/handler.rs
@@ -51,11 +51,7 @@ pub fn dispatch(
 /// That is, the state transition of message `i` must be applied before
 /// message `i+1` is validated. This is equivalent to calling
 /// `dispatch()` on each successively.
-pub fn validate<Ctx>(
-    ctx: &Ctx,
-    router: &mut impl Router,
-    msg: MsgEnvelope,
-) -> Result<(), RouterError>
+pub fn validate<Ctx>(ctx: &Ctx, router: &impl Router, msg: MsgEnvelope) -> Result<(), RouterError>
 where
     Ctx: ValidationContext,
 {