diff --git a/lib/src/chain/async_tree.rs b/lib/src/chain/async_tree.rs
index 32afabf450..7e9b2cb5f4 100644
--- a/lib/src/chain/async_tree.rs
+++ b/lib/src/chain/async_tree.rs
@@ -811,7 +811,10 @@ where
         assert!(match (self.input_finalized_index, new_best_block) {
             (Some(f), Some(b)) => self.non_finalized_blocks.is_ancestor(f, b),
             (Some(_), None) => false,
-            (None, Some(_)) => true,
+            (None, Some(b)) => {
+                assert!(self.non_finalized_blocks.contains(b));
+                true
+            }
             (None, None) => true,
         });
 
@@ -898,10 +901,13 @@ where
             };
 
             if let Some(new_finalized) = new_finalized {
-                // Update `input_finalized_index`.
+                // Update `input_finalized_index` and `input_best_block_index`.
                 if self.input_finalized_index == Some(new_finalized) {
                     self.input_finalized_index = None;
                 }
+                if self.input_best_block_index == Some(new_finalized) {
+                    self.input_best_block_index = None;
+                }
 
                 let mut pruned_blocks = Vec::new();
                 let mut pruned_finalized = None;
diff --git a/lib/src/chain/fork_tree.rs b/lib/src/chain/fork_tree.rs
index b758b135b6..126ab9f6d5 100644
--- a/lib/src/chain/fork_tree.rs
+++ b/lib/src/chain/fork_tree.rs
@@ -162,6 +162,11 @@ impl<T> ForkTree<T> {
         return_value.map(NodeIndex)
     }
 
+    /// Returns `true` if the given [`NodeIndex`] is valid.
+    pub fn contains(&self, index: NodeIndex) -> bool {
+        self.nodes.contains(index.0)
+    }
+
     /// Returns the value of the node with the given index.
     pub fn get(&self, index: NodeIndex) -> Option<&T> {
         self.nodes.get(index.0).map(|n| &n.data)
diff --git a/wasm-node/CHANGELOG.md b/wasm-node/CHANGELOG.md
index f4e0ad30ce..1625fb09a2 100644
--- a/wasm-node/CHANGELOG.md
+++ b/wasm-node/CHANGELOG.md
@@ -11,6 +11,7 @@
 - Fix the wrong `parentBlockHash` value being sent in `chainHead_v1_followEvent` notifications. ([#1791](https://github.com/smol-dot/smoldot/pull/1791))
 - Fix the `forbidWs` option being ignored when connecting to non-localhost addresses. Smoldot erroneously only took the value of `forbidNonLocalWs` in that situation. Connecting to a non-localhost address is now only done if both `forbidWs` and `forbidNonLocalWs` are `false`. ([#1790](https://github.com/smol-dot/smoldot/pull/1790))
 - The `finalizedBlockHash` field of the `initialized` event of `chainHead_v1_followEvent` notifications is now properly named `finalizedBlockHashes` and is now properly an array. ([#1792](https://github.com/smol-dot/smoldot/pull/1792))
+- Fix panic when calling the `system_health` JSON-RPC function when the finalized block is equal to the best block. ([#1798](https://github.com/smol-dot/smoldot/pull/1798))
 
 ## 2.0.24 - 2024-04-16