--- pngpread.c
+++ pngpread.c
@@ -1501,8 +1501,13 @@
 #endif
 
        png_strcpy((png_charp)chunk.name, (png_charp)png_ptr->chunk_name);
-       chunk.data = (png_bytep)png_malloc(png_ptr, length);
-       png_crc_read(png_ptr, chunk.data, length);
+       if (length == 0)
+           chunk.data = NULL;
+       else
+       {
+           chunk.data = (png_bytep)png_malloc(png_ptr, length);
+           png_crc_read(png_ptr, chunk.data, length);
+       }
        chunk.size = length;
 #if defined(PNG_READ_USER_CHUNKS_SUPPORTED)
        if(png_ptr->read_user_chunk_fn != NULL)
@@ -1520,7 +1525,7 @@
        else
 #endif
           png_set_unknown_chunks(png_ptr, info_ptr, &chunk, 1);
-       png_free(png_ptr, chunk.data);
+       if (chunk.data) png_free(png_ptr, chunk.data);
    }
    else
 #endif
--- pngrutil.c
+++ pngrutil.c
@@ -2193,10 +2193,16 @@
            length = (png_uint_32)65535L;
        }
 #endif
-       png_strcpy((png_charp)chunk.name, (png_charp)png_ptr->chunk_name);
-       chunk.data = (png_bytep)png_malloc(png_ptr, length);
+       png_memcpy((png_charp)chunk.name, (png_charp)png_ptr->chunk_name, png_sizeof(chunk.name));
+       chunk.name[png_sizeof(chunk.name)-1] = '\0';
        chunk.size = (png_size_t)length;
-       png_crc_read(png_ptr, (png_bytep)chunk.data, length);
+       if (length == 0)
+         chunk.data = NULL;
+       else
+       {
+         chunk.data = (png_bytep)png_malloc(png_ptr, length);
+         png_crc_read(png_ptr, (png_bytep)chunk.data, length);
+       }
 #if defined(PNG_READ_USER_CHUNKS_SUPPORTED)
        if(png_ptr->read_user_chunk_fn != NULL)
        {
@@ -2207,7 +2213,7 @@
                 if(png_handle_as_unknown(png_ptr, png_ptr->chunk_name) !=
                      PNG_HANDLE_CHUNK_ALWAYS)
                  {
-                   png_free(png_ptr, chunk.data);
+                   if(chunk.data) png_free(png_ptr, chunk.data);
                    png_chunk_error(png_ptr, "unknown critical chunk");
                  }
              png_set_unknown_chunks(png_ptr, info_ptr, &chunk, 1);
@@ -2216,7 +2222,7 @@
        else
 #endif
           png_set_unknown_chunks(png_ptr, info_ptr, &chunk, 1);
-       png_free(png_ptr, chunk.data);
+       if(chunk.data) png_free(png_ptr, chunk.data);
    }
    else
 #endif
--- pngset.c
+++ pngset.c
@@ -1023,19 +1023,26 @@
         png_unknown_chunkp to = np + info_ptr->unknown_chunks_num + i;
         png_unknown_chunkp from = unknowns + i;
 
-        png_strncpy((png_charp)to->name, (png_charp)from->name, 5);
-        to->data = (png_bytep)png_malloc_warn(png_ptr, from->size);
-        if (to->data == NULL)
-        {
-           png_warning(png_ptr, "Out of memory processing unknown chunk.");
-        }
+        png_memcpy((png_charp)to->name,
+                   (png_charp)from->name,
+                   png_sizeof(to->name));
+        to->name[png_sizeof(to->name)-1] = '\0';
+        to->size = from->size;
+        /* note our location in the read or write sequence */
+        to->location = (png_byte)(png_ptr->mode & 0xff);
+        if (from->size == 0)
+           to->data=NULL;
         else
         {
-           png_memcpy(to->data, from->data, from->size);
-           to->size = from->size;
-
-           /* note our location in the read or write sequence */
-           to->location = (png_byte)(png_ptr->mode & 0xff);
+           to->data = (png_bytep)png_malloc_warn(png_ptr, from->size);
+           if (to->data == NULL)
+           {
+              png_warning(png_ptr,
+		      "Out of memory processing unknown chunk.");
+              to->size=0;
+           }
+           else
+              png_memcpy(to->data, from->data, from->size);
         }
     }
 
--- pngwrite.c
+++ pngwrite.c
@@ -112,6 +112,8 @@
             ((up->name[3] & 0x20) || keep == PNG_HANDLE_CHUNK_ALWAYS ||
             (png_ptr->flags & PNG_FLAG_KEEP_UNSAFE_CHUNKS)))
          {
+            if (up->size == 0)
+               png_warning(png_ptr, "Writing zero-length unknown chunk");
             png_write_chunk(png_ptr, up->name, up->data, up->size);
          }
        }