diff --git a/ANNOUNCE b/ANNOUNCE
index cfac15a18..9cbbbd3a3 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -1,4 +1,4 @@
-Libpng 1.6.33beta02 - August 30, 2017
+Libpng 1.6.33beta02 - August 31, 2017
 
 This is not intended to be a public release. It will be replaced
 within a few weeks by a public version or by another test version.
@@ -30,9 +30,11 @@ Version 1.6.33beta01 [August 28, 2017]
   Fixed off-by-one error in png_do_check_palette_indexes() (Bug report
     by Mick P., Source Forge Issue #269).
 
-Version 1.6.33beta02 [August 30, 2017]
+Version 1.6.33beta02 [August 31, 2017]
   Initialize png_handler.row_ptr in contrib/oss-fuzz/libpng_read_fuzzer.cc
     to fix shortlived oss-fuzz issue 3234.
+  Compute a larger limit on IDAT because some applications write a deflate
+    buffer for each row (Bug report by Andrew Church).
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/CHANGES b/CHANGES
index 8b8f5b169..b04003468 100644
--- a/CHANGES
+++ b/CHANGES
@@ -6000,10 +6000,11 @@ Version 1.6.33beta01 [August 28, 2017]
   Fixed off-by-one error in png_do_check_palette_indexes() (Bug report
     by Mick P., Source Forge Issue #269).
 
-Version 1.6.33beta02 [August 30, 2017]
+Version 1.6.33beta02 [August 31, 2017]
   Initialize png_handler.row_ptr in contrib/oss-fuzz/libpng_read_fuzzer.cc
     to fix shortlived oss-fuzz issue 3234.
-
+  Compute a larger limit on IDAT because some applications write a deflate
+    buffer for each row (Bug report by Andrew Church).
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/pngrutil.c b/pngrutil.c
index a4fa71457..ccf5405e1 100644
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -3144,28 +3144,28 @@ png_check_chunk_length(png_const_structrp png_ptr, const png_uint_32 length)
 {
    png_alloc_size_t limit = PNG_UINT_31_MAX;
 
-   if (png_ptr->chunk_name != png_IDAT)
-   {
 # ifdef PNG_SET_USER_LIMITS_SUPPORTED
-      if (png_ptr->user_chunk_malloc_max > 0 &&
-          png_ptr->user_chunk_malloc_max < limit)
-         limit = png_ptr->user_chunk_malloc_max;
+   if (png_ptr->user_chunk_malloc_max > 0 &&
+       png_ptr->user_chunk_malloc_max < limit)
+      limit = png_ptr->user_chunk_malloc_max;
 # elif PNG_USER_CHUNK_MALLOC_MAX > 0
-      if (PNG_USER_CHUNK_MALLOC_MAX < limit)
-         limit = PNG_USER_CHUNK_MALLOC_MAX;
+   if (PNG_USER_CHUNK_MALLOC_MAX < limit)
+      limit = PNG_USER_CHUNK_MALLOC_MAX;
 # endif
-   }
-   else
+   if (png_ptr->chunk_name == png_IDAT)
    {
+      png_alloc_size_t idat_limit = PNG_UINT_31_MAX;
       size_t row_factor =
          (png_ptr->width * png_ptr->channels * (png_ptr->bit_depth > 8? 2: 1)
           + 1 + (png_ptr->interlaced? 6: 0));
       if (png_ptr->height > PNG_UINT_32_MAX/row_factor)
-         limit=PNG_UINT_31_MAX;
+         idat_limit=PNG_UINT_31_MAX;
       else
-         limit = png_ptr->height * row_factor;
-      limit += 6 + 5*(limit/32566+1); /* zlib+deflate overhead */
-      limit=limit < PNG_UINT_31_MAX? limit : PNG_UINT_31_MAX;
+         idat_limit = png_ptr->height * row_factor;
+      row_factor = row_factor > 32566? 32566 : row_factor;
+      idat_limit += 6 + 5*(idat_limit/row_factor+1); /* zlib+deflate overhead */
+      idat_limit=idat_limit < PNG_UINT_31_MAX? idat_limit : PNG_UINT_31_MAX;
+      limit = limit < idat_limit? idat_limit : limit;
    }
 
    if (length > limit)