diff --git a/tooling/ast_fuzzer/src/lib.rs b/tooling/ast_fuzzer/src/lib.rs
index 4de189661f1..516c58d444c 100644
--- a/tooling/ast_fuzzer/src/lib.rs
+++ b/tooling/ast_fuzzer/src/lib.rs
@@ -1,4 +1,5 @@
 #![forbid(unsafe_code)]
+#![warn(unreachable_pub)]
 #![warn(clippy::semicolon_if_nothing_returned)]
 #![cfg_attr(not(test), warn(unused_crate_dependencies, unused_extern_crates))]
 
diff --git a/tooling/ast_fuzzer/src/program/freq.rs b/tooling/ast_fuzzer/src/program/freq.rs
index c098a97c369..6f3a20340eb 100644
--- a/tooling/ast_fuzzer/src/program/freq.rs
+++ b/tooling/ast_fuzzer/src/program/freq.rs
@@ -36,7 +36,7 @@ pub(crate) struct Freq {
 }
 
 impl Freq {
-    pub fn new(u: &mut Unstructured, freqs: &Freqs) -> arbitrary::Result<Self> {
+    pub(crate) fn new(u: &mut Unstructured, freqs: &Freqs) -> arbitrary::Result<Self> {
         let x = u.choose_index(freqs.total())?;
         Ok(Self { freqs: freqs.clone(), x, accumulated: 0, disabled: 0 })
     }
@@ -44,7 +44,7 @@ impl Freq {
     /// Check if a key is enabled, based on the already checked cumulative values.
     ///
     /// To work correctly, `enabled` calls should come after `enabled_when`s.
-    pub fn enabled(&mut self, key: &str) -> bool {
+    pub(crate) fn enabled(&mut self, key: &str) -> bool {
         self.accumulated += self.freqs[key];
         self.passed()
     }
@@ -64,7 +64,7 @@ impl Freq {
     /// As a workaround, we should
     /// * check keys which are more likely to be disabled up front
     /// * have a default case at the end which is always enabled
-    pub fn enabled_when(&mut self, key: &str, cond: bool) -> bool {
+    pub(crate) fn enabled_when(&mut self, key: &str, cond: bool) -> bool {
         if cond {
             self.enabled(key)
         } else {
diff --git a/tooling/ast_fuzzer/src/program/func.rs b/tooling/ast_fuzzer/src/program/func.rs
index 3119405527c..36e38b0bfe5 100644
--- a/tooling/ast_fuzzer/src/program/func.rs
+++ b/tooling/ast_fuzzer/src/program/func.rs
@@ -42,7 +42,7 @@ pub(super) struct FunctionDeclaration {
 
 impl FunctionDeclaration {
     /// Generate a HIR function signature.
-    pub fn signature(&self) -> hir_def::function::FunctionSignature {
+    pub(super) fn signature(&self) -> hir_def::function::FunctionSignature {
         let param_types = self
             .params
             .iter()
@@ -140,7 +140,7 @@ pub(super) struct FunctionContext<'a> {
 }
 
 impl<'a> FunctionContext<'a> {
-    pub fn new(ctx: &'a mut Context, id: FuncId) -> Self {
+    pub(super) fn new(ctx: &'a mut Context, id: FuncId) -> Self {
         let decl = ctx.function_decl(id);
         let next_local_id = decl.params.iter().map(|p| p.0.0 + 1).max().unwrap_or_default();
         let budget = ctx.config.max_function_size;
@@ -206,7 +206,7 @@ impl<'a> FunctionContext<'a> {
     }
 
     /// Generate the function body.
-    pub fn gen_body(mut self, u: &mut Unstructured) -> arbitrary::Result<Expression> {
+    pub(super) fn gen_body(mut self, u: &mut Unstructured) -> arbitrary::Result<Expression> {
         // If we don't limit the budget according to the available data,
         // it gives us a lot of `false` and 0 and we end up with deep `!(!false)` if expressions.
         self.budget = self.budget.min(u.len());
@@ -220,7 +220,7 @@ impl<'a> FunctionContext<'a> {
 
     /// Generate the function body, wrapping a function call with literal arguments.
     /// This is used to test comptime functions, which can only take those.
-    pub fn gen_body_with_lit_call(
+    pub(super) fn gen_body_with_lit_call(
         mut self,
         u: &mut Unstructured,
         callee_id: FuncId,
diff --git a/tooling/ast_fuzzer/src/program/scope.rs b/tooling/ast_fuzzer/src/program/scope.rs
index e548b6dfdd9..30fd137e0d9 100644
--- a/tooling/ast_fuzzer/src/program/scope.rs
+++ b/tooling/ast_fuzzer/src/program/scope.rs
@@ -23,7 +23,7 @@ where
     K: Ord + Clone + Copy + Debug,
 {
     /// Create the initial scope from function parameters.
-    pub fn new(vars: impl Iterator<Item = (K, bool, Name, Type)>) -> Self {
+    pub(super) fn new(vars: impl Iterator<Item = (K, bool, Name, Type)>) -> Self {
         let mut scope = Self { variables: im::OrdMap::new(), producers: im::OrdMap::new() };
         for (id, mutable, name, typ) in vars {
             scope.add(id, mutable, name, typ);
@@ -72,7 +72,7 @@ where
     }
 
     /// Choose a random producer of a type, if there is one.
-    pub fn choose_producer(
+    pub(super) fn choose_producer(
         &self,
         u: &mut Unstructured,
         typ: &Type,
@@ -87,7 +87,7 @@ where
     }
 
     /// Get a variable in scope.
-    pub fn get_variable(&self, id: &K) -> &Variable {
+    pub(super) fn get_variable(&self, id: &K) -> &Variable {
         self.variables.get(id).unwrap_or_else(|| panic!("variable doesn't exist: {:?}", id))
     }
 }
@@ -97,22 +97,22 @@ where
     K: Ord,
 {
     /// Check if there are any variables in scope.
-    pub fn is_empty(&self) -> bool {
+    pub(super) fn is_empty(&self) -> bool {
         self.variables.is_empty()
     }
 
     /// Iterate the variables in scope.
-    pub fn variables(&self) -> impl ExactSizeIterator<Item = (&K, &Variable)> {
+    pub(super) fn variables(&self) -> impl ExactSizeIterator<Item = (&K, &Variable)> {
         self.variables.iter()
     }
 
     /// Iterate the IDs of the variables in scope.
-    pub fn variable_ids(&self) -> impl ExactSizeIterator<Item = &K> {
+    pub(super) fn variable_ids(&self) -> impl ExactSizeIterator<Item = &K> {
         self.variables.keys()
     }
 
     /// Iterate the types we can produce from other variables.
-    pub fn types_produced(&self) -> impl ExactSizeIterator<Item = &Type> {
+    pub(super) fn types_produced(&self) -> impl ExactSizeIterator<Item = &Type> {
         self.producers.keys()
     }
 }
@@ -125,34 +125,34 @@ where
     K: Ord + Clone + Copy + Debug,
 {
     /// Create a stack from the base variables.
-    pub fn new(vars: impl Iterator<Item = (K, bool, Name, Type)>) -> Self {
+    pub(super) fn new(vars: impl Iterator<Item = (K, bool, Name, Type)>) -> Self {
         Self(vec![Scope::new(vars)])
     }
 
     /// The top scope in the stack.
-    pub fn current(&self) -> &Scope<K> {
+    pub(super) fn current(&self) -> &Scope<K> {
         self.0.last().expect("there is always the base layer")
     }
 
     /// Push a new scope on top of the current one.
-    pub fn enter(&mut self) {
+    pub(super) fn enter(&mut self) {
         // Instead of shallow cloning an immutable map, we could loop through layers when looking up variables.
         self.0.push(self.current().clone());
     }
 
     /// Remove the last layer of block variables.
-    pub fn exit(&mut self) {
+    pub(super) fn exit(&mut self) {
         self.0.pop();
         assert!(!self.0.is_empty(), "never pop the base layer");
     }
 
     /// Add a new variable to the current scope.
-    pub fn add(&mut self, id: K, mutable: bool, name: String, typ: Type) {
+    pub(super) fn add(&mut self, id: K, mutable: bool, name: String, typ: Type) {
         self.0.last_mut().expect("there is always a layer").add(id, mutable, name, typ);
     }
 
     /// Remove a variable from all scopes.
-    pub fn remove(&mut self, id: &K) {
+    pub(super) fn remove(&mut self, id: &K) {
         for scope in self.0.iter_mut() {
             scope.remove(id);
         }