diff --git a/src/hwm_lm75.c b/src/hwm_lm75.c
index 0d937c194..8463fbc78 100644
--- a/src/hwm_lm75.c
+++ b/src/hwm_lm75.c
@@ -128,7 +128,7 @@ lm75_read(lm75_t *dev, uint8_t reg)
     /* The AS99127F hardware monitor uses the addresses of its LM75 devices
        to access some of its proprietary registers. Pass this operation on to
        the main monitor address through an internal SMBus call, if necessary. */
-    if ((reg >= 0x80) && (dev->as99127f_smbus_addr))
+    if (((reg & 0xf8) != 0x50) && (dev->as99127f_smbus_addr))
     	ret = smbus_read_byte_cmd(dev->as99127f_smbus_addr, reg);
     else
     	ret = dev->regs[reg & 0x7];
@@ -191,7 +191,7 @@ lm75_write(lm75_t *dev, uint8_t reg, uint8_t val)
     /* The AS99127F hardware monitor uses the addresses of its LM75 devices
        to access some of its proprietary registers. Pass this operation on to
        the main monitor address through an internal SMBus call, if necessary. */
-    if ((reg >= 0x80) && (dev->as99127f_smbus_addr)) {
+    if (((reg & 0xf8) != 0x50) && (dev->as99127f_smbus_addr)) {
     	smbus_write_byte_cmd(dev->as99127f_smbus_addr, reg, val);
     	return 1;
     }
diff --git a/src/hwm_lm78.c b/src/hwm_lm78.c
index e303779a7..bf474db9e 100644
--- a/src/hwm_lm78.c
+++ b/src/hwm_lm78.c
@@ -180,11 +180,11 @@ lm78_read(lm78_t *dev, uint8_t reg, uint8_t bank)
     uint8_t ret = 0;
     lm75_t *lm75;
 
-    if (((reg & 0xf0) == 0x50) && (bank != 0)) {
+    if (((reg & 0xf8) == 0x50) && (bank != 0)) {
     	/* LM75 registers */
     	lm75 = device_get_priv(dev->lm75[bank - 1]);
     	if (lm75)
-    		ret = lm75_read(lm75, reg & 0xf);
+    		ret = lm75_read(lm75, reg);
     } else {
     	/* regular registers */
     	if ((reg == 0x4f) && (dev->local & LM78_WINBOND)) /* special case for two-byte vendor ID register */
@@ -192,7 +192,7 @@ lm78_read(lm78_t *dev, uint8_t reg, uint8_t bank)
     	else if ((reg >= 0x60) && (reg <= 0x7f)) /* read auto-increment value RAM registers from their non-auto-increment locations */
     		ret = dev->regs[reg & 0x3f];
     	else if ((reg >= 0x80) && (reg <= 0x92)) /* AS99127F mirrors [0x00:0x12] to [0x80:0x92] */
-    		ret = dev->regs[reg - 0x7f];
+    		ret = dev->regs[reg & 0x7f];
     	else
     		ret = dev->regs[reg];
     }
@@ -260,11 +260,11 @@ lm78_write(lm78_t *dev, uint8_t reg, uint8_t val, uint8_t bank)
 
     lm78_log("LM78: write(%02X, %d, %02X)\n", reg, bank, val);
 
-    if (((reg & 0xf0) == 0x50) && (bank != 0)) {
+    if (((reg & 0xf8) == 0x50) && (bank != 0)) {
     	/* LM75 registers */
     	lm75 = device_get_priv(dev->lm75[bank - 1]);
     	if (lm75)
-    		lm75_write(lm75, reg & 0xf, val);
+    		lm75_write(lm75, reg, val);
     	return 1;
     }