diff --git a/pngrutil.c b/pngrutil.c
index 1de7427..72a8b5e 100644
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -503,7 +503,7 @@ void /* PRIVATE */
 png_handle_PLTE(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
 {
    png_color palette[PNG_MAX_PALETTE_LENGTH];
-   int num, i;
+   int max_palette_length, num, i;
 #ifdef PNG_POINTER_INDEXING_SUPPORTED
    png_colorp pal_ptr;
 #endif
@@ -555,8 +555,21 @@ png_handle_PLTE(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
       }
    }
 
+   /* The cast is safe because 'length' is less than 3*PNG_MAX_PALETTE_LENGTH */
    num = (int)length / 3;
 
+   /* If the palette has 256 or fewer entries but is too large for the bit depth,
+    * we don't issue an error, to preserve the behavior of previous libpng versions.
+    * We silently truncate the unused extra palette entries here.
+    */
+   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
+      max_palette_length = (1 << png_ptr->bit_depth);
+   else
+      max_palette_length = PNG_MAX_PALETTE_LENGTH;
+
+   if (num > max_palette_length)
+      num = max_palette_length;
+
 #ifdef PNG_POINTER_INDEXING_SUPPORTED
    for (i = 0, pal_ptr = palette; i < num; i++, pal_ptr++)
    {
@@ -589,7 +602,7 @@ png_handle_PLTE(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
    if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
 #endif
    {
-      png_crc_finish(png_ptr, 0);
+      png_crc_finish(png_ptr, (int) length - num * 3);
    }
 #ifndef PNG_READ_OPT_PLTE_SUPPORTED
    else if (png_crc_error(png_ptr))  /* Only if we have a CRC error */
@@ -1097,7 +1110,7 @@ png_handle_iCCP(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
    /* There should be at least one zero (the compression type byte)
     * following the separator, and we should be on it
     */
-   if ( profile >= png_ptr->chunkdata + slength - 1)
+   if ( slength < 1 || profile >= png_ptr->chunkdata + slength - 1)
    {
       png_free(png_ptr, png_ptr->chunkdata);
       png_ptr->chunkdata = NULL;
@@ -1225,7 +1238,7 @@ png_handle_sPLT(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
    ++entry_start;
 
    /* A sample depth should follow the separator, and we should be on it  */
-   if (entry_start > (png_bytep)png_ptr->chunkdata + slength - 2)
+   if (slength < 2 || entry_start > (png_bytep)png_ptr->chunkdata + slength - 2)
    {
       png_free(png_ptr, png_ptr->chunkdata);
       png_ptr->chunkdata = NULL;
@@ -1699,7 +1712,7 @@ png_handle_pCAL(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
 
    /* We need to have at least 12 bytes after the purpose string
       in order to get the parameter information. */
-   if (endptr <= buf + 12)
+   if (slength < 12 || endptr <= buf + 12)
    {
       png_warning(png_ptr, "Invalid pCAL data");
       png_free(png_ptr, png_ptr->chunkdata);
@@ -2155,7 +2168,7 @@ png_handle_zTXt(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
       /* Empty loop */ ;
 
    /* zTXt must have some text after the chunkdataword */
-   if (text >= png_ptr->chunkdata + slength - 2)
+   if (slength < 2 || text >= png_ptr->chunkdata + slength - 2)
    {
       png_warning(png_ptr, "Truncated zTXt chunk");
       png_free(png_ptr, png_ptr->chunkdata);
@@ -2281,7 +2294,7 @@ png_handle_iTXt(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
     * keyword
     */
 
-   if (lang >= png_ptr->chunkdata + slength - 3)
+   if (slength < 3 || lang >= png_ptr->chunkdata + slength - 3)
    {
       png_warning(png_ptr, "Truncated iTXt chunk");
       png_free(png_ptr, png_ptr->chunkdata);
diff --git a/pngset.c b/pngset.c
index 7a47b1e..54ac931 100644
--- a/pngset.c
+++ b/pngset.c
@@ -446,12 +446,17 @@ png_set_PLTE(png_structp png_ptr, png_infop info_ptr,
    png_colorp palette, int num_palette)
 {
 
+   png_uint_32 max_palette_length;
+
    png_debug1(1, "in %s storage function", "PLTE");
 
    if (png_ptr == NULL || info_ptr == NULL)
       return;
 
-   if (num_palette < 0 || num_palette > PNG_MAX_PALETTE_LENGTH)
+   max_palette_length = (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE) ?
+      (1 << info_ptr->bit_depth) : PNG_MAX_PALETTE_LENGTH;
+
+   if (num_palette < 0 || num_palette > (int) max_palette_length)
    {
       if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
          png_error(png_ptr, "Invalid palette length");
diff --git a/pngwutil.c b/pngwutil.c
index c75f53e..80128d6 100644
--- a/pngwutil.c
+++ b/pngwutil.c
@@ -575,17 +575,20 @@ png_write_PLTE(png_structp png_ptr, png_colorp palette, png_uint_32 num_pal)
 #ifdef PNG_USE_LOCAL_ARRAYS
    PNG_PLTE;
 #endif
-   png_uint_32 i;
+   png_uint_32 max_palette_length, i;
    png_colorp pal_ptr;
    png_byte buf[3];
 
    png_debug(1, "in png_write_PLTE");
 
+   max_palette_length = (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE) ?
+      (1 << png_ptr->bit_depth) : PNG_MAX_PALETTE_LENGTH;
+
    if ((
 #ifdef PNG_MNG_FEATURES_SUPPORTED
         !(png_ptr->mng_features_permitted & PNG_FLAG_MNG_EMPTY_PLTE) &&
 #endif
-        num_pal == 0) || num_pal > 256)
+        num_pal == 0) || num_pal > max_palette_length)
    {
      if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
      {