diff --git a/src/eval/cache.rs b/src/eval/cache.rs
index 8b552280..c792a4ff 100644
--- a/src/eval/cache.rs
+++ b/src/eval/cache.rs
@@ -2,9 +2,9 @@
 
 use crate::func::CallableFunction;
 use crate::{Identifier, StaticVec};
-use std::collections::BTreeMap;
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
+use std::{collections::BTreeMap, marker::PhantomData};
 
 /// _(internals)_ An entry in a function resolution cache.
 /// Exported under the `internals` feature only.
@@ -29,14 +29,14 @@ pub type FnResolutionCache = BTreeMap<u64, Option<FnResolutionCacheEntry>>;
 /// The following caches are contained inside this type:
 /// * A stack of [function resolution caches][FnResolutionCache]
 #[derive(Debug, Clone)]
-pub struct Caches(StaticVec<FnResolutionCache>);
+pub struct Caches<'a>(StaticVec<FnResolutionCache>, PhantomData<&'a ()>);
 
-impl Caches {
+impl Caches<'_> {
     /// Create an empty [`Caches`].
     #[inline(always)]
     #[must_use]
     pub const fn new() -> Self {
-        Self(StaticVec::new_const())
+        Self(StaticVec::new_const(), PhantomData)
     }
     /// Get the number of function resolution cache(s) in the stack.
     #[inline(always)]
diff --git a/src/eval/eval_context.rs b/src/eval/eval_context.rs
index 42041fb7..150b19e4 100644
--- a/src/eval/eval_context.rs
+++ b/src/eval/eval_context.rs
@@ -7,7 +7,7 @@ use std::prelude::v1::*;
 
 /// Context of a script evaluation process.
 #[derive(Debug)]
-pub struct EvalContext<'a, 's, 'ps, 'g, 'pg, 'c, 't, 'pt> {
+pub struct EvalContext<'a, 's, 'ps, 'g, 'pg, 'c, 'pc, 't, 'pt> {
     /// The current [`Engine`].
     engine: &'a Engine,
     /// The current [`Scope`].
@@ -15,7 +15,7 @@ pub struct EvalContext<'a, 's, 'ps, 'g, 'pg, 'c, 't, 'pt> {
     /// The current [`GlobalRuntimeState`].
     global: &'g mut GlobalRuntimeState<'pg>,
     /// The current [caches][Caches], if available.
-    caches: Option<&'c mut Caches>,
+    caches: Option<&'c mut Caches<'pc>>,
     /// The current stack of imported [modules][Module].
     lib: &'a [&'a Module],
     /// The current bound `this` pointer, if any.
@@ -24,7 +24,7 @@ pub struct EvalContext<'a, 's, 'ps, 'g, 'pg, 'c, 't, 'pt> {
     level: usize,
 }
 
-impl<'a, 's, 'ps, 'g, 'pg, 'c, 't, 'pt> EvalContext<'a, 's, 'ps, 'g, 'pg, 'c, 't, 'pt> {
+impl<'a, 's, 'ps, 'g, 'pg, 'c, 'pc, 't, 'pt> EvalContext<'a, 's, 'ps, 'g, 'pg, 'c, 'pc, 't, 'pt> {
     /// Create a new [`EvalContext`].
     #[inline(always)]
     #[must_use]
@@ -32,7 +32,7 @@ impl<'a, 's, 'ps, 'g, 'pg, 'c, 't, 'pt> EvalContext<'a, 's, 'ps, 'g, 'pg, 'c, 't
         engine: &'a Engine,
         scope: &'s mut Scope<'ps>,
         global: &'g mut GlobalRuntimeState<'pg>,
-        caches: Option<&'c mut Caches>,
+        caches: Option<&'c mut Caches<'pc>>,
         lib: &'a [&'a Module],
         this_ptr: &'t mut Option<&'pt mut Dynamic>,
         level: usize,
diff --git a/src/optimizer.rs b/src/optimizer.rs
index 69731719..fe3e9101 100644
--- a/src/optimizer.rs
+++ b/src/optimizer.rs
@@ -55,7 +55,7 @@ struct OptimizerState<'a> {
     /// The global runtime state.
     global: GlobalRuntimeState<'a>,
     /// Function resolution caches.
-    caches: Caches,
+    caches: Caches<'a>,
     /// [Module][crate::Module] containing script-defined functions.
     #[cfg(not(feature = "no_function"))]
     lib: &'a [&'a crate::Module],