--- mformat.c.orig	2013-01-08 23:14:21.000000000 +0100
+++ mformat.c	2018-08-11 12:43:23.357909111 +0200
@@ -541,11 +541,23 @@ static void calc_cluster_size(struct Fs_
 				FAT_SIZE(16, Fs->sector_size, max_clusters);
 			break;
 		case 32:
-			Fs->cluster_size = 8;
-			/* According to
-			 * http://support.microsoft.com/support/kb/articles/q154/9/97.asp
-			 * Micro$oft does not support FAT32 with less than 4K
+			/*
+			   FAT32 cluster sizes for disks with 512 block size
+			   according to Microsoft specification fatgen103.doc:
+			
+			   32.5 MB - 260 MB   cluster_size =  1
+			    260 MB -   8 GB   cluster_size =  8
+			      8 GB -  16 GB   cluster_size = 16
+			     16 GB -  32 GB   cluster_size = 32
+			     32 GB -   2 TB   cluster_size = 64
+			
+			   Below calculation is generalized and does not depend
+			   on 512 block size.
 			 */
+			Fs->cluster_size = tot_sectors > 32*1024*1024*2 ? 64 :
+			                   tot_sectors > 16*1024*1024*2 ? 32 :
+			                   tot_sectors >  8*1024*1024*2 ? 16 :
+			                   tot_sectors >     260*1024*2 ? 8 : 1;
 			return;
 		default:
 			fprintf(stderr,"Bad fat size\n");
@@ -564,13 +576,13 @@ static void calc_cluster_size(struct Fs_
 	/* double the cluster size until we can fill up the disk with
 	 * the maximal number of sectors of this size */
 	while(Fs->cluster_size * max_clusters  + max_fat_size < rem_sect) {
+		Fs->cluster_size <<= 1;
 		if(Fs->cluster_size > 64) {
 			/* bigger than 64. Should fit */
 			fprintf(stderr,
 				"Internal error while calculating cluster size\n");
 			exit(1);
 		}
-		Fs->cluster_size <<= 1;
 	}
 }
 
@@ -680,15 +692,15 @@ static void calc_fs_parameters_32(unsign
 		boot->boot.descr = 0xf8;
 	else
 		boot->boot.descr = 0xf0;
-	if(!Fs->cluster_size)
-		/* According to
-		 * http://www.microsoft.com/kb/articles/q154/9/97.htm,
-		 * Micro$oft does not support FAT32 with less than 4K
-		 */
-		Fs->cluster_size = 8;
 
 	Fs->dir_len = 0;
+	calc_cluster_size(Fs, tot_sectors, 32);
 	Fs->num_clus = tot_sectors / Fs->cluster_size;
+	/* Maximal number of clusters on FAT32 is 268435446 */
+	if (Fs->num_clus > 268435446) {
+		fprintf(stderr, "Too many clusters\n");
+		exit(1);
+	}
 	set_fat32(Fs);
 	calc_fat_size(Fs, tot_sectors);
 	set_word(boot->boot.fatlen, 0);
@@ -1189,6 +1201,11 @@ void mformat(int argc, char **argv, int
 	if(tot_sectors == 0) {
 		unsigned long sect_per_track = used_dev.heads*used_dev.sectors;
 		tot_sectors = used_dev.tracks*sect_per_track - used_dev.hidden%sect_per_track;
+		/* Number of sectors must fit into 32bit value */
+		if (tot_sectors > 0xFFFFFFFF) {
+			fprintf(stderr, "Too many sectors\n");
+			exit(1);
+		}
 	}
 
 	/* create the image file if needed */