diff --git a/h_malloc.c b/h_malloc.c
index 6f848f7..0aaae9a 100644
--- a/h_malloc.c
+++ b/h_malloc.c
@@ -1642,7 +1642,7 @@ EXPORT size_t h_malloc_usable_size(H_MALLOC_USABLE_SIZE_CONST void *p) {
     return size;
 }
 
-EXPORT size_t h_malloc_object_size(void *p) {
+EXPORT size_t h_malloc_object_size(const void *p) {
     if (p == NULL) {
         return 0;
     }
@@ -1699,7 +1699,7 @@ EXPORT size_t h_malloc_object_size(void *p) {
     return size;
 }
 
-EXPORT size_t h_malloc_object_size_fast(void *p) {
+EXPORT size_t h_malloc_object_size_fast(const void *p) {
     if (p == NULL) {
         return 0;
     }
diff --git a/include/h_malloc.h b/include/h_malloc.h
index fdc7083..5824abb 100644
--- a/include/h_malloc.h
+++ b/include/h_malloc.h
@@ -104,10 +104,10 @@ void h_malloc_enable(void);
 // hardened_malloc extensions
 
 // return an upper bound on object size for any pointer based on malloc metadata
-size_t h_malloc_object_size(void *ptr);
+size_t h_malloc_object_size(const void *ptr);
 
 // similar to malloc_object_size, but avoiding locking so the results are much more limited
-size_t h_malloc_object_size_fast(void *ptr);
+size_t h_malloc_object_size_fast(const void *ptr);
 
 // The free function with an extra parameter for passing the size requested at
 // allocation time.