diff --git a/external/io_grib2/g2lib/dec_png.c b/external/io_grib2/g2lib/dec_png.c
index aa85184b36..a33c0c0ac6 100644
--- a/external/io_grib2/g2lib/dec_png.c
+++ b/external/io_grib2/g2lib/dec_png.c
@@ -88,7 +88,7 @@ int DEC_PNG(unsigned char *pngbuf,g2int *width,g2int *height,char *cout)
 
 /*    Set new custom read function    */
 
-    png_set_read_fn(png_ptr,(voidp)&read_io_ptr,(png_rw_ptr)user_read_data);
+    png_set_read_fn(png_ptr,(png_voidp)&read_io_ptr,(png_rw_ptr)user_read_data);
 /*     png_init_io(png_ptr, fptr);   */
 
 /*     Read and decode PNG stream   */
diff --git a/external/io_grib2/g2lib/enc_png.c b/external/io_grib2/g2lib/enc_png.c
index 7d2ef1d287..97d0b961a9 100644
--- a/external/io_grib2/g2lib/enc_png.c
+++ b/external/io_grib2/g2lib/enc_png.c
@@ -88,7 +88,7 @@ int ENC_PNG(char *data,g2int *width,g2int *height,g2int *nbits,char *pngbuf)
 
 /*    Set new custom write functions    */
 
-    png_set_write_fn(png_ptr,(voidp)&write_io_ptr,(png_rw_ptr)user_write_data,
+    png_set_write_fn(png_ptr,(png_voidp)&write_io_ptr,(png_rw_ptr)user_write_data,
                     (png_flush_ptr)user_flush_data);
 /*    png_init_io(png_ptr, fptr);   */
 /*    png_set_compression_level(png_ptr, Z_BEST_COMPRESSION);  */