diff --git a/prog/dump/i2cset.8 b/prog/dump/i2cset.8
index 44746c71..3996c94e 100644
--- a/prog/dump/i2cset.8
+++ b/prog/dump/i2cset.8
@@ -10,6 +10,7 @@ i2cset \- set I2C registers
 .I data-address
 .I value
 .RI [ mode ]
+.RI [ mask ]
 .br
 .B i2cset
 .B -V
@@ -42,6 +43,11 @@ The \fImode\fR parameter, if specified, is one of the letters \fBb\fP or
 respectively. If the \fImode\fR parameter is omitted, i2cset defaults to byte
 mode. The \fIvalue\fR provided must be within range for the specified data
 type (0x00-0xFF for bytes, 0x0000-0xFFFF for words).
+.PP
+The \fImask\fR parameter, if specified, describes which bits of \fIvalue\fR
+will be actually written to \fIdata-address\fR. Bits set to 1 in the mask
+are taken from \fIvalue\fR, while bits set to 0 will be read from
+\fIdata-address\fR and thus preserved by the operation.
 
 .SH WARNING
 i2cset can be extremely dangerous if used improperly. It can confuse your
diff --git a/prog/dump/i2cset.c b/prog/dump/i2cset.c
index af4afae5..ba35527a 100644
--- a/prog/dump/i2cset.c
+++ b/prog/dump/i2cset.c
@@ -33,7 +33,7 @@ void help(void) __attribute__ ((noreturn));
 void help(void)
 {
 	fprintf(stderr, "Syntax: i2cset [-y] I2CBUS CHIP-ADDRESS DATA-ADDRESS "
-	        "VALUE [MODE]\n"
+	        "VALUE [MODE] [MASK]\n"
 	        "        i2cset -V\n"
 	        "  MODE is 'b[yte]' or 'w[ord]' (default b)\n"
 	        "  I2CBUS is an integer\n");
@@ -45,7 +45,7 @@ int main(int argc, char *argv[])
 {
 	char *end;
 	int res, i2cbus, address, size, file;
-	int value, daddress;
+	int value, daddress, vmask = 0;
 	int e1;
 	char filename[20];
 	long funcs;
@@ -110,6 +110,14 @@ int main(int argc, char *argv[])
 		help();
 	}
 
+	if (argc >= flags + 7) {
+		vmask = strtol(argv[flags+6], &end, 0);
+		if (*end || vmask == 0) {
+			fprintf(stderr, "Error: Data value mask invalid!\n");
+			help();
+		}
+	}
+
 	if (value < 0
 	 || (size == I2C_SMBUS_BYTE_DATA && value > 0xff)
 	 || (size == I2C_SMBUS_WORD_DATA && value > 0xffff)) {
@@ -171,8 +179,9 @@ int main(int argc, char *argv[])
 		}
 
 		fprintf(stderr, "I will write to device file %s, chip address "
-		        "0x%02x, data address\n0x%02x, data 0x%02x, mode "
+		        "0x%02x, data address\n0x%02x, data 0x%02x%s, mode "
 		        "%s.\n", filename, address, daddress, value,
+			vmask ? " (masked)" : "",
 			size == I2C_SMBUS_BYTE_DATA ? "byte" : "word");
 
 		fprintf(stderr, "Continue? [%s] ", dont ? "y/N" : "Y/n");
@@ -184,6 +193,43 @@ int main(int argc, char *argv[])
 		}
 	}
 
+	if (vmask) {
+		int oldvalue;
+
+		if (size == I2C_SMBUS_WORD_DATA) {
+			oldvalue = i2c_smbus_read_word_data(file, daddress);
+		} else {
+			oldvalue = i2c_smbus_read_byte_data(file, daddress);
+		}
+
+		if (oldvalue < 0) {
+			fprintf(stderr, "Error: Failed to read old value\n");
+			exit(1);
+		}
+
+		value = (value & vmask) | (oldvalue & ~vmask);
+
+		if (!yes) {
+			char s[2];
+			
+			fprintf(stderr, "Old value 0x%0*x, write mask "
+				"0x%0*x: Will write 0x%0*x to register "
+				"0x%02x\n",
+				size == I2C_SMBUS_WORD_DATA ? 4 : 2, oldvalue,
+				size == I2C_SMBUS_WORD_DATA ? 4 : 2, vmask,
+				size == I2C_SMBUS_WORD_DATA ? 4 : 2, value,
+				daddress);
+
+			fprintf(stderr, "Continue? [Y/n] ");
+			fflush(stderr);
+			fgets(s, 2, stdin);
+			if (s[0] != '\n' && s[0] != 'y' && s[0] != 'Y') {
+				fprintf(stderr, "Aborting on user request.\n");
+				exit(0);
+			}
+		}
+	}
+
 	e1 = 0;
 	if (size == I2C_SMBUS_WORD_DATA) {
 		res = i2c_smbus_write_word_data(file, daddress, value);