diff --git a/ANNOUNCE b/ANNOUNCE
index 5aa888f8b..8811428c9 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -35,6 +35,9 @@ Version 1.5.30beta01 [August 28, 2017]
 Version 1.5.30beta02 [September 3, 2017]
   Compute a larger limit on IDAT because some applications write a deflate
     buffer for each row (Bug report by Andrew Church).
+  Fixed incorrect typecast of some arguments to png_malloc() and
+    png_calloc() that were png_uint_32 instead of png_alloc_size_t
+    (Bug report by "irwir" in Github libpng issue #175).
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/CHANGES b/CHANGES
index 570cb4bf2..8ad1181fa 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4563,6 +4563,9 @@ Version 1.5.30beta01 [August 28, 2017]
 Version 1.5.30beta02 [September 3, 2017]
   Compute a larger limit on IDAT because some applications write a deflate
     buffer for each row (Bug report by Andrew Church).
+  Fixed incorrect typecast of some arguments to png_malloc() and
+    png_calloc() that were png_uint_32 instead of png_alloc_size_t
+    (Bug report by "irwir" in Github libpng issue #175).
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/pngrtran.c b/pngrtran.c
index ad1e7a634..9889b9abb 100644
--- a/pngrtran.c
+++ b/pngrtran.c
@@ -396,7 +396,7 @@ png_set_quantize(png_structp png_ptr, png_colorp palette,
       int i;
 
       png_ptr->quantize_index = (png_bytep)png_malloc(png_ptr,
-          (png_uint_32)(num_palette * png_sizeof(png_byte)));
+          (png_alloc_size_t)(num_palette * png_sizeof(png_byte)));
       for (i = 0; i < num_palette; i++)
          png_ptr->quantize_index[i] = (png_byte)i;
    }
@@ -413,7 +413,7 @@ png_set_quantize(png_structp png_ptr, png_colorp palette,
 
          /* Initialize an array to sort colors */
          png_ptr->quantize_sort = (png_bytep)png_malloc(png_ptr,
-             (png_uint_32)(num_palette * png_sizeof(png_byte)));
+             (png_alloc_size_t)(num_palette * png_sizeof(png_byte)));
 
          /* Initialize the quantize_sort array */
          for (i = 0; i < num_palette; i++)
@@ -547,9 +547,9 @@ png_set_quantize(png_structp png_ptr, png_colorp palette,
 
          /* Initialize palette index arrays */
          png_ptr->index_to_palette = (png_bytep)png_malloc(png_ptr,
-             (png_uint_32)(num_palette * png_sizeof(png_byte)));
+             (png_alloc_size_t)(num_palette * png_sizeof(png_byte)));
          png_ptr->palette_to_index = (png_bytep)png_malloc(png_ptr,
-             (png_uint_32)(num_palette * png_sizeof(png_byte)));
+             (png_alloc_size_t)(num_palette * png_sizeof(png_byte)));
 
          /* Initialize the sort array */
          for (i = 0; i < num_palette; i++)
@@ -589,7 +589,7 @@ png_set_quantize(png_structp png_ptr, png_colorp palette,
                   {
 
                      t = (png_dsortp)png_malloc_warn(png_ptr,
-                         (png_uint_32)(png_sizeof(png_dsort)));
+                         (png_alloc_size_t)(png_sizeof(png_dsort)));
 
                      if (t == NULL)
                          break;
@@ -716,7 +716,7 @@ png_set_quantize(png_structp png_ptr, png_colorp palette,
       png_ptr->palette_lookup = (png_bytep)png_calloc(png_ptr,
           (png_uint_32)(num_entries * png_sizeof(png_byte)));
 
-      distance = (png_bytep)png_malloc(png_ptr, (png_uint_32)(num_entries *
+      distance = (png_bytep)png_malloc(png_ptr, (png_alloc_size_t)(num_entries *
           png_sizeof(png_byte)));
 
       png_memset(distance, 0xff, num_entries * png_sizeof(png_byte));