diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f1274bdb..568b452f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -2,7 +2,7 @@ name: CI
 on: [pull_request]
 
 env:
-  RUST_VERSION: 1.75.0
+  RUST_VERSION: 1.81.0
 
 jobs:
   build:
diff --git a/canbench-bin/tests/tests.rs b/canbench-bin/tests/tests.rs
index d323c5c8..1b4f927f 100644
--- a/canbench-bin/tests/tests.rs
+++ b/canbench-bin/tests/tests.rs
@@ -279,17 +279,17 @@ fn reports_scopes_in_new_benchmark() {
 
 Benchmark: bench_scope_new (new)
   total:
-    instructions: 3411 (new)
+    instructions: 3579 (new)
     heap_increase: 0 pages (new)
     stable_memory_increase: 0 pages (new)
 
   scope_1 (scope):
-    instructions: 1002 (new)
+    instructions: 1286 (new)
     heap_increase: 0 pages (new)
     stable_memory_increase: 0 pages (new)
 
   scope_2 (scope):
-    instructions: 787 (new)
+    instructions: 740 (new)
     heap_increase: 0 pages (new)
     stable_memory_increase: 0 pages (new)
 
@@ -356,17 +356,17 @@ fn reports_scopes_in_existing_benchmark() {
 
 Benchmark: bench_scope_exists
   total:
-    instructions: 3411 (regressed from 0)
+    instructions: 3579 (regressed from 0)
     heap_increase: 0 pages (no change)
     stable_memory_increase: 0 pages (no change)
 
   scope_1 (scope):
-    instructions: 1002 (regressed by 25.25%)
+    instructions: 1286 (regressed by 60.75%)
     heap_increase: 0 pages (improved by 100.00%)
     stable_memory_increase: 0 pages (no change)
 
   scope_2 (scope):
-    instructions: 787 (new)
+    instructions: 740 (new)
     heap_increase: 0 pages (new)
     stable_memory_increase: 0 pages (new)
 
@@ -400,7 +400,7 @@ fn benchmark_works_with_init_args() {
 
 Benchmark: state_check
   total:
-    instructions: 804 (no change)
+    instructions: 867 (no change)
     heap_increase: 0 pages (no change)
     stable_memory_increase: 0 pages (no change)
 
@@ -423,7 +423,7 @@ fn benchmark_stable_writes() {
 
 Benchmark: write_stable_memory (new)
   total:
-    instructions: 49.09 K (new)
+    instructions: 49.12 K (new)
     heap_increase: 0 pages (new)
     stable_memory_increase: 1 pages (new)
 
diff --git a/canbench-rs/src/lib.rs b/canbench-rs/src/lib.rs
index 100189a9..639f7471 100644
--- a/canbench-rs/src/lib.rs
+++ b/canbench-rs/src/lib.rs
@@ -409,7 +409,7 @@ use std::cell::RefCell;
 use std::collections::BTreeMap;
 
 thread_local! {
-    static SCOPES: RefCell<BTreeMap<&'static str, Measurement>> = RefCell::new(BTreeMap::new());
+    static SCOPES: RefCell<BTreeMap<&'static str, Measurement>> = const { RefCell::new(BTreeMap::new()) };
 }
 
 /// The results of a benchmark.
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
index b30063f1..5c6d171a 100644
--- a/rust-toolchain.toml
+++ b/rust-toolchain.toml
@@ -1,3 +1,3 @@
 [toolchain]
-channel = "1.75.0"  # NOTE: remember to update CI as well.
+channel = "1.81.0"  # NOTE: remember to update CI as well.
 targets = ["wasm32-unknown-unknown"]
diff --git a/tests/init_arg/canbench_results.yml b/tests/init_arg/canbench_results.yml
index 49a50a7e..2e45d97a 100644
--- a/tests/init_arg/canbench_results.yml
+++ b/tests/init_arg/canbench_results.yml
@@ -4,6 +4,6 @@ benches:
   state_check:
     total:
       heap_delta: 0
-      instructions: 804
+      instructions: 867
       stable_memory_delta: 0
 version: 0.1.0
diff --git a/tests/init_arg/src/main.rs b/tests/init_arg/src/main.rs
index 4fba7bdb..5f66fde2 100644
--- a/tests/init_arg/src/main.rs
+++ b/tests/init_arg/src/main.rs
@@ -2,7 +2,7 @@ use canbench_rs::bench;
 use std::cell::RefCell;
 
 thread_local! {
-    static STATE: RefCell<String> = RefCell::new(String::new());
+    static STATE: RefCell<String> = const { RefCell::new(String::new()) };
 }
 // A benchmark that prints the state.
 #[bench]