diff --git a/stb_image.h b/stb_image.h
index 397b400..647f8a9 100644
--- a/stb_image.h
+++ b/stb_image.h
@@ -4275,12 +4275,13 @@ static int stbi__parse_png_file(stbi__png *z, int scan, int req_comp)
          }
 
          case STBI__PNG_TYPE('I','E','N','D'): {
-            stbi__uint32 raw_len;
+            stbi__uint32 raw_len, bpl;
             if (first) return stbi__err("first not IHDR", "Corrupt PNG");
             if (scan != STBI__SCAN_load) return 1;
             if (z->idata == NULL) return stbi__err("no IDAT","Corrupt PNG");
             // initial guess for decoded data size to avoid unnecessary reallocs
-            raw_len = s->img_x * s->img_y * s->img_n /* pixels */ + s->img_y /* filter mode per row */;
+            bpl = (s->img_x * depth + 7) / 8; // bytes per line, per component
+            raw_len = bpl * s->img_y * s->img_n /* pixels */ + s->img_y /* filter mode per row */;
             z->expanded = (stbi_uc *) stbi_zlib_decode_malloc_guesssize_headerflag((char *) z->idata, ioff, raw_len, (int *) &raw_len, !is_iphone);
             if (z->expanded == NULL) return 0; // zlib should set error
             STBI_FREE(z->idata); z->idata = NULL;