diff --git a/src/H5Centry.c b/src/H5Centry.c
index 41fbe0cd9e8..9b93a96057c 100644
--- a/src/H5Centry.c
+++ b/src/H5Centry.c
@@ -1571,7 +1571,7 @@ H5C__serialize_single_entry(H5F_t *f, H5C_t *cache_ptr, H5C_cache_entry_t *entry
         if (NULL == (entry_ptr->image_ptr = H5MM_malloc(entry_ptr->size + H5C_IMAGE_EXTRA_SPACE)))
             HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "memory allocation failed for on disk image buffer");
 #if H5C_DO_MEMORY_SANITY_CHECKS
-        H5MM_memcpy(((uint8_t *)entry_ptr->image_ptr) + image_size, H5C_IMAGE_SANITY_VALUE,
+        H5MM_memcpy(((uint8_t *)entry_ptr->image_ptr) + entry_ptr->size, H5C_IMAGE_SANITY_VALUE,
                     H5C_IMAGE_EXTRA_SPACE);
 #endif /* H5C_DO_MEMORY_SANITY_CHECKS */
     }  /* end if */
diff --git a/src/H5Cimage.c b/src/H5Cimage.c
index 87df542bdea..c99c612d7b3 100644
--- a/src/H5Cimage.c
+++ b/src/H5Cimage.c
@@ -2682,7 +2682,8 @@ H5C__reconstruct_cache_entry(const H5F_t *f, H5C_t *cache_ptr, const uint8_t **b
     if (NULL == (pf_entry_ptr->image_ptr = H5MM_malloc(pf_entry_ptr->size + H5C_IMAGE_EXTRA_SPACE)))
         HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, NULL, "memory allocation failed for on disk image buffer");
 #if H5C_DO_MEMORY_SANITY_CHECKS
-    H5MM_memcpy(((uint8_t *)pf_entry_ptr->image_ptr) + size, H5C_IMAGE_SANITY_VALUE, H5C_IMAGE_EXTRA_SPACE);
+    H5MM_memcpy(((uint8_t *)pf_entry_ptr->image_ptr) + pf_entry_ptr->size, H5C_IMAGE_SANITY_VALUE,
+                H5C_IMAGE_EXTRA_SPACE);
 #endif /* H5C_DO_MEMORY_SANITY_CHECKS */
 
     /* Copy the entry image from the cache image block */