diff --git a/ANNOUNCE b/ANNOUNCE
index a045d0ed81cac4bbd676834a26b2a5dfcb5f53ad..789b7153d24861d9947f35bfd5395b3d2cd25ba4 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -109,6 +109,8 @@ Version 1.5.3beta07 [May 11, 2011]
   Moved macro definitions for PNG_HAVE_IHDR, PNG_HAVE_PLTE, and PNG_AFTER_IDAT
     from pngpriv.h to png.h because they must be visible to applications
     that call png_set_unknown_chunks().
+  Check for up->location !PNG_AFTER_IDAT when writing unknown chunks
+    before IDAT.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net:
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diff --git a/CHANGES b/CHANGES
index 3e24f3adc7f87ec41e9eb412ae936d8746504de3..0312d86bfda4492b28514b701391b49a6d4d4e2c 100644
--- a/CHANGES
+++ b/CHANGES
@@ -3368,6 +3368,8 @@ Version 1.5.3beta07 [May 11, 2011]
   Moved macro definitions for PNG_HAVE_IHDR, PNG_HAVE_PLTE, and PNG_AFTER_IDAT
     from pngpriv.h to png.h because they must be visible to applications
     that call png_set_unknown_chunks().
+  Check for up->location !PNG_AFTER_IDAT when writing unknown chunks
+    before IDAT.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/pngwrite.c b/pngwrite.c
index 3e854cb1fb47c30d1f459f9f7d0b3d3fd7214457..c36b0767f8f719b5b6168a19c8ce4f42360aa92f 100644
--- a/pngwrite.c
+++ b/pngwrite.c
@@ -99,8 +99,10 @@ png_write_info_before_PLTE(png_structp png_ptr, png_infop info_ptr)
          int keep = png_handle_as_unknown(png_ptr, up->name);
 
          if (keep != PNG_HANDLE_CHUNK_NEVER &&
-             up->location && !(up->location & PNG_HAVE_PLTE) &&
+             up->location &&
+             !(up->location & PNG_HAVE_PLTE) &&
              !(up->location & PNG_HAVE_IDAT) &&
+             !(up->location & PNG_AFTER_IDAT) &&
              ((up->name[3] & 0x20) || keep == PNG_HANDLE_CHUNK_ALWAYS ||
              (png_ptr->flags & PNG_FLAG_KEEP_UNSAFE_CHUNKS)))
          {
@@ -273,8 +275,10 @@ png_write_info(png_structp png_ptr, png_infop info_ptr)
       {
          int keep = png_handle_as_unknown(png_ptr, up->name);
          if (keep != PNG_HANDLE_CHUNK_NEVER &&
-             up->location && (up->location & PNG_HAVE_PLTE) &&
+             up->location &&
+             (up->location & PNG_HAVE_PLTE) &&
              !(up->location & PNG_HAVE_IDAT) &&
+             !(up->location & PNG_AFTER_IDAT) &&
              ((up->name[3] & 0x20) || keep == PNG_HANDLE_CHUNK_ALWAYS ||
              (png_ptr->flags & PNG_FLAG_KEEP_UNSAFE_CHUNKS)))
          {
@@ -380,7 +384,8 @@ png_write_end(png_structp png_ptr, png_infop info_ptr)
       {
          int keep = png_handle_as_unknown(png_ptr, up->name);
          if (keep != PNG_HANDLE_CHUNK_NEVER &&
-             up->location && (up->location & PNG_AFTER_IDAT) &&
+             up->location &&
+             (up->location & PNG_AFTER_IDAT) &&
              ((up->name[3] & 0x20) || keep == PNG_HANDLE_CHUNK_ALWAYS ||
              (png_ptr->flags & PNG_FLAG_KEEP_UNSAFE_CHUNKS)))
          {