diff --git a/libpng-manual.txt b/libpng-manual.txt
index f0ebb5dc7..032548e24 100644
--- a/libpng-manual.txt
+++ b/libpng-manual.txt
@@ -637,7 +637,7 @@ callback function:
 
       /* also ignore unused known chunks: */
       png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
-         (int)sizeof(unused_chunks)/5);
+         (int)(sizeof unused_chunks)/5);
     #endif
 
 User limits
@@ -989,7 +989,7 @@ where row_pointers is an array of pointers to the pixel data for each row:
 If you know your image size and pixel size ahead of time, you can allocate
 row_pointers prior to calling png_read_png() with
 
-   if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
+   if (height > PNG_UINT_32_MAX/(sizeof (png_byte))
       png_error (png_ptr,
           "Image is too tall to process in memory");
 
@@ -998,7 +998,7 @@ row_pointers prior to calling png_read_png() with
           "Image is too wide to process in memory");
 
    row_pointers = png_malloc(png_ptr,
-       height*png_sizeof(png_bytep));
+       height*(sizeof (png_bytep)));
 
    for (int i=0; i<height, i++)
       row_pointers[i]=NULL;  /* security precaution */
diff --git a/libpng.3 b/libpng.3
index 33aec6196..56634f6c1 100644
--- a/libpng.3
+++ b/libpng.3
@@ -1131,7 +1131,7 @@ callback function:
 
       /* also ignore unused known chunks: */
       png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
-         (int)sizeof(unused_chunks)/5);
+         (int)(sizeof unused_chunks)/5);
     #endif
 
 .SS User limits
@@ -1483,7 +1483,7 @@ where row_pointers is an array of pointers to the pixel data for each row:
 If you know your image size and pixel size ahead of time, you can allocate
 row_pointers prior to calling png_read_png() with
 
-   if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
+   if (height > PNG_UINT_32_MAX/(sizeof (png_byte))
       png_error (png_ptr,
           "Image is too tall to process in memory");
 
@@ -1492,7 +1492,7 @@ row_pointers prior to calling png_read_png() with
           "Image is too wide to process in memory");
 
    row_pointers = png_malloc(png_ptr,
-       height*png_sizeof(png_bytep));
+       height*(sizeof (png_bytep)));
 
    for (int i=0; i<height, i++)
       row_pointers[i]=NULL;  /* security precaution */