--- a/pngrutil.c	2020-05-22 15:22:29.217401425 +0800
+++ b/pngrutil.c	2020-05-22 15:29:51.151515952 +0800
@@ -361,8 +361,15 @@
          /* Success (maybe) - really uncompress the chunk. */
          png_size_t new_size = 0;
 
-         png_charp text = png_malloc_warn(png_ptr,
-             prefix_size + expanded_size + 1);
+         png_charp text = NULL;
+         /* Need to check for both truncation (64-bit platforms) and integer
+          * overflow.
+          */
+         if (prefix_size + expanded_size > prefix_size &&
+             prefix_size + expanded_size < 0xffffffffU)
+         {
+            text = png_malloc_warn(png_ptr, prefix_size + expanded_size + 1);
+         }
 
          if (text != NULL)
          {