diff --git a/api/optional.cc b/api/optional.cc
index 94126170a5..0f74bd2446 100644
--- a/api/optional.cc
+++ b/api/optional.cc
@@ -15,7 +15,7 @@ namespace optional_internal {
 
 #if RTC_HAS_ASAN
 
-void* FunctionThatDoesNothingImpl(void* x) {
+const void* FunctionThatDoesNothingImpl(const void* x) {
   return x;
 }
 
diff --git a/api/optional.h b/api/optional.h
index 9221f2c0b5..ba06831a29 100644
--- a/api/optional.h
+++ b/api/optional.h
@@ -33,18 +33,18 @@ namespace optional_internal {
 // This is a non-inlined function. The optimizer can't see inside it.  It
 // prevents the compiler from generating optimized code that reads value_ even
 // if it is unset. Although safe, this causes memory sanitizers to complain.
-void* FunctionThatDoesNothingImpl(void*);
+const void* FunctionThatDoesNothingImpl(const void*);
 
 template <typename T>
-inline T* FunctionThatDoesNothing(T* x) {
-  return reinterpret_cast<T*>(
-      FunctionThatDoesNothingImpl(reinterpret_cast<void*>(x)));
+inline const T* FunctionThatDoesNothing(T* x) {
+  return reinterpret_cast<const T*>(
+      FunctionThatDoesNothingImpl(reinterpret_cast<const void*>(x)));
 }
 
 #else
 
 template <typename T>
-inline T* FunctionThatDoesNothing(T* x) {
+inline const T* FunctionThatDoesNothing(T* x) {
   return x;
 }