diff --git a/src/inspector/inspector.cc b/src/inspector/inspector.cc
index 7957c85..1564d37 100644
--- a/src/inspector/inspector.cc
+++ b/src/inspector/inspector.cc
@@ -46,9 +46,9 @@
 Inspector::Inspector(ast::Module& module, Namer* namer)
     : module_(module), namer_(namer), namer_is_owned_(false) {}
 
-Inspector::Inspector(ast::Module& module)
+Inspector::Inspector(const ast::Module& module)
     : module_(module),
-      namer_(new MangleNamer(&module)),
+      namer_(new MangleNamer(&module_)),
       namer_is_owned_(true) {}
 
 Inspector::~Inspector() {
diff --git a/src/inspector/inspector.h b/src/inspector/inspector.h
index 4a17b8d..9ec0f00 100644
--- a/src/inspector/inspector.h
+++ b/src/inspector/inspector.h
@@ -77,7 +77,7 @@
   Inspector(ast::Module& module, Namer* namer);
   /// Constructor
   /// @param module Shader module to extract information from.
-  explicit Inspector(ast::Module& module);
+  explicit Inspector(const ast::Module& module);
   ~Inspector();
 
   /// @returns error messages from the Inspector
diff --git a/src/namer.cc b/src/namer.cc
index d5f304d..9215b39 100644
--- a/src/namer.cc
+++ b/src/namer.cc
@@ -22,7 +22,7 @@
 
 namespace tint {
 
-Namer::Namer(ast::Module* mod) : module_(mod) {}
+Namer::Namer(const ast::Module* mod) : module_(mod) {}
 
 Namer::~Namer() = default;
 
@@ -46,7 +46,7 @@
   return name;
 }
 
-MangleNamer::MangleNamer(ast::Module* mod) : Namer(mod) {}
+MangleNamer::MangleNamer(const ast::Module* mod) : Namer(mod) {}
 
 MangleNamer::~MangleNamer() = default;
 
@@ -54,7 +54,7 @@
   return sym.to_str();
 }
 
-UnsafeNamer::UnsafeNamer(ast::Module* mod) : Namer(mod) {}
+UnsafeNamer::UnsafeNamer(const ast::Module* mod) : Namer(mod) {}
 
 UnsafeNamer::~UnsafeNamer() = default;
 
diff --git a/src/namer.h b/src/namer.h
index 7745cf0..e2b671a 100644
--- a/src/namer.h
+++ b/src/namer.h
@@ -28,7 +28,7 @@
  public:
   /// Constructor
   /// @param mod the module this namer works with
-  explicit Namer(ast::Module* mod);
+  explicit Namer(const ast::Module* mod);
   /// Destructor
   virtual ~Namer();
 
@@ -52,7 +52,7 @@
   bool IsUsed(const std::string& name);
 
   /// The module storing the symbol table
-  ast::Module* module_ = nullptr;
+  const ast::Module* module_ = nullptr;
 
  private:
   // The list of names taken by the remapper
@@ -64,7 +64,7 @@
  public:
   /// Constructor
   /// @param mod the module to retrieve names from
-  explicit MangleNamer(ast::Module* mod);
+  explicit MangleNamer(const ast::Module* mod);
   /// Destructor
   ~MangleNamer() override;
 
@@ -81,7 +81,7 @@
  public:
   /// Constructor
   /// @param mod the module to retrieve names from
-  explicit UnsafeNamer(ast::Module* mod);
+  explicit UnsafeNamer(const ast::Module* mod);
   /// Destructor
   ~UnsafeNamer() override;
 
diff --git a/src/writer/test_namer.cc b/src/writer/test_namer.cc
index 0ab1a7d..1c13148 100644
--- a/src/writer/test_namer.cc
+++ b/src/writer/test_namer.cc
@@ -17,7 +17,7 @@
 namespace tint {
 namespace writer {
 
-TestNamer::TestNamer(ast::Module* mod) : Namer(mod) {}
+TestNamer::TestNamer(const ast::Module* mod) : Namer(mod) {}
 
 TestNamer::~TestNamer() = default;
 
diff --git a/src/writer/test_namer.h b/src/writer/test_namer.h
index 44a7e68..da08c2c 100644
--- a/src/writer/test_namer.h
+++ b/src/writer/test_namer.h
@@ -27,7 +27,7 @@
  public:
   /// Constructor
   /// @param mod the module to retrieve names from
-  explicit TestNamer(ast::Module* mod);
+  explicit TestNamer(const ast::Module* mod);
   /// Destructor
   ~TestNamer() override;