diff --git a/doc/man/st-flash.1 b/doc/man/st-flash.1
index 252ffcba8..77a8bb550 100644
--- a/doc/man/st-flash.1
+++ b/doc/man/st-flash.1
@@ -53,6 +53,14 @@ TODO
 TODO
 .RS
 .RE
+.TP
+.B --flash=\f[I]size\f[]
+Override the device's normal flash size, where size is the flash size in bytes. 
+It can be specified in decimal, octal or hexadecimal.
+The size argument can optionally be followed by 'k' for KB or 'm' for MB.
+Examples --flash=128k or --flash=0x080k.
+.RS
+.RE
 .SH EXAMPLES
 .PP
 Flash \f[C]firmware.bin\f[] to device
diff --git a/doc/man/st-flash.md b/doc/man/st-flash.md
index 4eacb7a07..d1844976c 100644
--- a/doc/man/st-flash.md
+++ b/doc/man/st-flash.md
@@ -49,6 +49,10 @@ reset
 --serial *iSerial*
 :   TODO
 
+--flash=fsize
+:   Where fsize is the size in decimal, octal, or hex followed by an optional multiplier 
+'k' for KB, or 'm' for MB.
+Use a leading "0x" to specify hexadecimal, or a leading zero for octal.
 
 # EXAMPLES
 Flash `firmware.bin` to device
diff --git a/include/stlink/tools/flash.h b/include/stlink/tools/flash.h
index 6a7b05484..35b3a4251 100644
--- a/include/stlink/tools/flash.h
+++ b/include/stlink/tools/flash.h
@@ -20,9 +20,10 @@ struct flash_opts
     int reset;
     int log_level;
     enum flash_format format;
+    size_t flash_size;	/* --flash=n[k][m] */
 };
 
-#define FLASH_OPTS_INITIALIZER {0, NULL, {}, NULL, 0, 0, 0, 0, 0 }
+#define FLASH_OPTS_INITIALIZER {0, NULL, {}, NULL, 0, 0, 0, 0, 0, 0 }
 
 int flash_get_opts(struct flash_opts* o, int ac, char** av);
 
diff --git a/src/tools/flash.c b/src/tools/flash.c
index f2c186e95..6fe365f88 100644
--- a/src/tools/flash.c
+++ b/src/tools/flash.c
@@ -29,12 +29,13 @@ static void cleanup(int signum) {
 
 static void usage(void)
 {
-    puts("stlinkv1 command line: ./st-flash [--debug] [--reset] [--format <format>] {read|write} /dev/sgX <path> <addr> <size>");
+    puts("stlinkv1 command line: ./st-flash [--debug] [--reset] [--format <format>] [--flash=<fsize>] {read|write} /dev/sgX <path> <addr> <size>");
     puts("stlinkv1 command line: ./st-flash [--debug] /dev/sgX erase");
-    puts("stlinkv2 command line: ./st-flash [--debug] [--reset] [--serial <serial>] [--format <format>] {read|write} <path> <addr> <size>");
+    puts("stlinkv2 command line: ./st-flash [--debug] [--reset] [--serial <serial>] [--format <format>] [--flash=<fsize>] {read|write} <path> <addr> <size>");
     puts("stlinkv2 command line: ./st-flash [--debug] [--serial <serial>] erase");
     puts("stlinkv2 command line: ./st-flash [--debug] [--serial <serial>] reset");
     puts("                       Use hex format for addr, <serial> and <size>.");
+    puts("                       fsize: Use decimal, octal or hex by prefix 0xXXX for hex, optionally followed by k=KB, or m=MB (eg. --flash=128k)");
     puts("                       Format may be 'binary' (default) or 'ihex', although <addr> must be specified for binary format only.");
     puts("                       ./st-flash [--version]");
 }
@@ -64,6 +65,11 @@ int main(int ac, char** av)
     if (sl == NULL)
         return -1;
 
+    if ( o.flash_size != 0u && o.flash_size != sl->flash_size ) {
+        sl->flash_size = o.flash_size;
+        printf("Forcing flash size: --flash=0x%08zX\n",sl->flash_size);
+    }
+
     sl->verbose = o.log_level;
 
     connected_stlink = sl;
diff --git a/src/tools/flash_opts.c b/src/tools/flash_opts.c
index c98424348..4fa39de4c 100644
--- a/src/tools/flash_opts.c
+++ b/src/tools/flash_opts.c
@@ -77,7 +77,30 @@ int flash_get_opts(struct flash_opts* o, int ac, char** av)
             else
                 return -1;
         }
-        else {
+	else if ( starts_with(av[0], "--flash=") ) {
+		const char *arg = av[0] + strlen("--flash=");
+		char *ep = 0;
+
+		o->flash_size = (uint32_t)strtoul(arg,&ep,0);
+		while ( *ep ) {
+			switch ( *ep++ ) {
+			case 0:
+				break;
+			case 'k':
+			case 'K':
+				o->flash_size *= 1024u;
+				break;
+			case 'm':
+			case 'M':
+				o->flash_size *= 1024u * 1024u;
+				break;
+			default:
+				fprintf(stderr,"Invalid --flash=%s\n",arg);
+				return -1;
+			}
+		}
+	}
+	else {
             break;  // non-option found
         }