diff --git a/hw/net/dp8393x.c b/hw/net/dp8393x.c
index 17f0338..efa33ad 100644
--- a/hw/net/dp8393x.c
+++ b/hw/net/dp8393x.c
@@ -174,6 +174,52 @@ typedef struct dp8393xState {
     AddressSpace as;
 } dp8393xState;
 
+/* Accessor functions for values which are formed by
+ * concatenating two 16 bit device registers. By putting these
+ * in their own functions with a uint32_t return type we avoid the
+ * pitfall of implicit sign extension where ((x << 16) | y) is a
+ * signed 32 bit integer that might get sign-extended to a 64 bit integer.
+ */
+static uint32_t dp8393x_cdp(dp8393xState *s)
+{
+    return (s->regs[SONIC_URRA] << 16) | s->regs[SONIC_CDP];
+}
+
+static uint32_t dp8393x_crba(dp8393xState *s)
+{
+    return (s->regs[SONIC_CRBA1] << 16) | s->regs[SONIC_CRBA0];
+}
+
+static uint32_t dp8393x_crda(dp8393xState *s)
+{
+    return (s->regs[SONIC_URDA] << 16) | s->regs[SONIC_CRDA];
+}
+
+static uint32_t dp8393x_rbwc(dp8393xState *s)
+{
+    return (s->regs[SONIC_RBWC1] << 16) | s->regs[SONIC_RBWC0];
+}
+
+static uint32_t dp8393x_rrp(dp8393xState *s)
+{
+    return (s->regs[SONIC_URRA] << 16) | s->regs[SONIC_RRP];
+}
+
+static uint32_t dp8393x_tsa(dp8393xState *s)
+{
+    return (s->regs[SONIC_TSA1] << 16) | s->regs[SONIC_TSA0];
+}
+
+static uint32_t dp8393x_ttda(dp8393xState *s)
+{
+    return (s->regs[SONIC_UTDA] << 16) | s->regs[SONIC_TTDA];
+}
+
+static uint32_t dp8393x_wt(dp8393xState *s)
+{
+    return s->regs[SONIC_WT1] << 16 | s->regs[SONIC_WT0];
+}
+
 static void dp8393x_update_irq(dp8393xState *s)
 {
     int level = (s->regs[SONIC_IMR] & s->regs[SONIC_ISR]) ? 1 : 0;
@@ -203,8 +249,7 @@ static void dp8393x_do_load_cam(dp8393xState *s)
 
     while (s->regs[SONIC_CDC] & 0x1f) {
         /* Fill current entry */
-        address_space_rw(&s->as,
-            (s->regs[SONIC_URRA] << 16) | s->regs[SONIC_CDP],
+        address_space_rw(&s->as, dp8393x_cdp(s),
             MEMTXATTRS_UNSPECIFIED, (uint8_t *)data, size, 0);
         s->cam[index][0] = data[1 * width] & 0xff;
         s->cam[index][1] = data[1 * width] >> 8;
@@ -222,8 +267,7 @@ static void dp8393x_do_load_cam(dp8393xState *s)
     }
 
     /* Read CAM enable */
-    address_space_rw(&s->as,
-        (s->regs[SONIC_URRA] << 16) | s->regs[SONIC_CDP],
+    address_space_rw(&s->as, dp8393x_cdp(s),
         MEMTXATTRS_UNSPECIFIED, (uint8_t *)data, size, 0);
     s->regs[SONIC_CE] = data[0 * width];
     DPRINTF("load cam done. cam enable mask 0x%04x\n", s->regs[SONIC_CE]);
@@ -242,8 +286,7 @@ static void dp8393x_do_read_rra(dp8393xState *s)
     /* Read memory */
     width = (s->regs[SONIC_DCR] & SONIC_DCR_DW) ? 2 : 1;
     size = sizeof(uint16_t) * 4 * width;
-    address_space_rw(&s->as,
-        (s->regs[SONIC_URRA] << 16) | s->regs[SONIC_RRP],
+    address_space_rw(&s->as, dp8393x_rrp(s),
         MEMTXATTRS_UNSPECIFIED, (uint8_t *)data, size, 0);
 
     /* Update SONIC registers */
@@ -292,7 +335,7 @@ static void dp8393x_set_next_tick(dp8393xState *s)
         return;
     }
 
-    ticks = s->regs[SONIC_WT1] << 16 | s->regs[SONIC_WT0];
+    ticks = dp8393x_wt(s);
     s->wt_last_update = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
     delay = NANOSECONDS_PER_SECOND * ticks / 5000000;
     timer_mod(s->watchdog, s->wt_last_update + delay);
@@ -309,7 +352,7 @@ static void dp8393x_update_wt_regs(dp8393xState *s)
     }
 
     elapsed = s->wt_last_update - qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
-    val = s->regs[SONIC_WT1] << 16 | s->regs[SONIC_WT0];
+    val = dp8393x_wt(s);
     val -= elapsed / 5000000;
     s->regs[SONIC_WT1] = (val >> 16) & 0xffff;
     s->regs[SONIC_WT0] = (val >> 0)  & 0xffff;
@@ -356,12 +399,11 @@ static void dp8393x_do_transmit_packets(dp8393xState *s)
 
     while (1) {
         /* Read memory */
-        DPRINTF("Transmit packet at %08x\n",
-                (s->regs[SONIC_UTDA] << 16) | s->regs[SONIC_CTDA]);
         size = sizeof(uint16_t) * 6 * width;
         s->regs[SONIC_TTDA] = s->regs[SONIC_CTDA];
+        DPRINTF("Transmit packet at %08x\n", dp8393x_ttda(s));
         address_space_rw(&s->as,
-            ((s->regs[SONIC_UTDA] << 16) | s->regs[SONIC_TTDA]) + sizeof(uint16_t) * width,
+            dp8393x_ttda(s) + sizeof(uint16_t) * width,
             MEMTXATTRS_UNSPECIFIED, (uint8_t *)data, size, 0);
         tx_len = 0;
 
@@ -386,8 +428,7 @@ static void dp8393x_do_transmit_packets(dp8393xState *s)
             if (tx_len + len > sizeof(s->tx_buffer)) {
                 len = sizeof(s->tx_buffer) - tx_len;
             }
-            address_space_rw(&s->as,
-                (s->regs[SONIC_TSA1] << 16) | s->regs[SONIC_TSA0],
+            address_space_rw(&s->as, dp8393x_tsa(s),
                 MEMTXATTRS_UNSPECIFIED, &s->tx_buffer[tx_len], len, 0);
             tx_len += len;
 
@@ -396,7 +437,7 @@ static void dp8393x_do_transmit_packets(dp8393xState *s)
                 /* Read next fragment details */
                 size = sizeof(uint16_t) * 3 * width;
                 address_space_rw(&s->as,
-                    ((s->regs[SONIC_UTDA] << 16) | s->regs[SONIC_TTDA]) + sizeof(uint16_t) * (4 + 3 * i) * width,
+                    dp8393x_ttda(s) + sizeof(uint16_t) * (4 + 3 * i) * width,
                     MEMTXATTRS_UNSPECIFIED, (uint8_t *)data, size, 0);
                 s->regs[SONIC_TSA0] = data[0 * width];
                 s->regs[SONIC_TSA1] = data[1 * width];
@@ -430,14 +471,16 @@ static void dp8393x_do_transmit_packets(dp8393xState *s)
         data[0 * width] = s->regs[SONIC_TCR] & 0x0fff; /* status */
         size = sizeof(uint16_t) * width;
         address_space_rw(&s->as,
-            (s->regs[SONIC_UTDA] << 16) | s->regs[SONIC_TTDA],
+            dp8393x_ttda(s),
             MEMTXATTRS_UNSPECIFIED, (uint8_t *)data, size, 1);
 
         if (!(s->regs[SONIC_CR] & SONIC_CR_HTX)) {
             /* Read footer of packet */
             size = sizeof(uint16_t) * width;
             address_space_rw(&s->as,
-                ((s->regs[SONIC_UTDA] << 16) | s->regs[SONIC_TTDA]) + sizeof(uint16_t) * (4 + 3 * s->regs[SONIC_TFC]) * width,
+                dp8393x_ttda(s) +
+                             sizeof(uint16_t) *
+                             (4 + 3 * s->regs[SONIC_TFC]) * width,
                 MEMTXATTRS_UNSPECIFIED, (uint8_t *)data, size, 0);
             s->regs[SONIC_CTDA] = data[0 * width] & ~0x1;
             if (data[0 * width] & 0x1) {
@@ -700,7 +743,7 @@ static ssize_t dp8393x_receive(NetClientState *nc, const uint8_t * buf,
     if (s->regs[SONIC_LLFA] & 0x1) {
         /* Are we still in resource exhaustion? */
         size = sizeof(uint16_t) * 1 * width;
-        address = ((s->regs[SONIC_URDA] << 16) | s->regs[SONIC_CRDA]) + sizeof(uint16_t) * 5 * width;
+        address = dp8393x_crda(s) + sizeof(uint16_t) * 5 * width;
         address_space_rw(&s->as, address, MEMTXATTRS_UNSPECIFIED,
                          (uint8_t *)data, size, 0);
         if (data[0 * width] & 0x1) {
@@ -719,8 +762,8 @@ static ssize_t dp8393x_receive(NetClientState *nc, const uint8_t * buf,
     checksum = cpu_to_le32(crc32(0, buf, rx_len));
 
     /* Put packet into RBA */
-    DPRINTF("Receive packet at %08x\n", (s->regs[SONIC_CRBA1] << 16) | s->regs[SONIC_CRBA0]);
-    address = (s->regs[SONIC_CRBA1] << 16) | s->regs[SONIC_CRBA0];
+    DPRINTF("Receive packet at %08x\n", dp8393x_crba(s));
+    address = dp8393x_crba(s);
     address_space_rw(&s->as, address,
         MEMTXATTRS_UNSPECIFIED, (uint8_t *)buf, rx_len, 1);
     address += rx_len;
@@ -729,13 +772,13 @@ static ssize_t dp8393x_receive(NetClientState *nc, const uint8_t * buf,
     rx_len += 4;
     s->regs[SONIC_CRBA1] = address >> 16;
     s->regs[SONIC_CRBA0] = address & 0xffff;
-    available = (s->regs[SONIC_RBWC1] << 16) | s->regs[SONIC_RBWC0];
+    available = dp8393x_rbwc(s);
     available -= rx_len / 2;
     s->regs[SONIC_RBWC1] = available >> 16;
     s->regs[SONIC_RBWC0] = available & 0xffff;
 
     /* Update status */
-    if (((s->regs[SONIC_RBWC1] << 16) | s->regs[SONIC_RBWC0]) < s->regs[SONIC_EOBC]) {
+    if (dp8393x_rbwc(s) < s->regs[SONIC_EOBC]) {
         s->regs[SONIC_RCR] |= SONIC_RCR_LPKT;
     }
     s->regs[SONIC_RCR] |= packet_type;
@@ -746,20 +789,19 @@ static ssize_t dp8393x_receive(NetClientState *nc, const uint8_t * buf,
     }
 
     /* Write status to memory */
-    DPRINTF("Write status at %08x\n", (s->regs[SONIC_URDA] << 16) | s->regs[SONIC_CRDA]);
+    DPRINTF("Write status at %08x\n", dp8393x_crda(s));
     data[0 * width] = s->regs[SONIC_RCR]; /* status */
     data[1 * width] = rx_len; /* byte count */
     data[2 * width] = s->regs[SONIC_TRBA0]; /* pkt_ptr0 */
     data[3 * width] = s->regs[SONIC_TRBA1]; /* pkt_ptr1 */
     data[4 * width] = s->regs[SONIC_RSC]; /* seq_no */
     size = sizeof(uint16_t) * 5 * width;
-    address_space_rw(&s->as, (s->regs[SONIC_URDA] << 16) | s->regs[SONIC_CRDA],
+    address_space_rw(&s->as, dp8393x_crda(s),
         MEMTXATTRS_UNSPECIFIED, (uint8_t *)data, size, 1);
 
     /* Move to next descriptor */
     size = sizeof(uint16_t) * width;
-    address_space_rw(&s->as,
-        ((s->regs[SONIC_URDA] << 16) | s->regs[SONIC_CRDA]) + sizeof(uint16_t) * 5 * width,
+    address_space_rw(&s->as, dp8393x_crda(s) + sizeof(uint16_t) * 5 * width,
         MEMTXATTRS_UNSPECIFIED, (uint8_t *)data, size, 0);
     s->regs[SONIC_LLFA] = data[0 * width];
     if (s->regs[SONIC_LLFA] & 0x1) {
@@ -767,8 +809,7 @@ static ssize_t dp8393x_receive(NetClientState *nc, const uint8_t * buf,
         s->regs[SONIC_ISR] |= SONIC_ISR_RDE;
     } else {
         data[0 * width] = 0; /* in_use */
-        address_space_rw(&s->as,
-            ((s->regs[SONIC_URDA] << 16) | s->regs[SONIC_CRDA]) + sizeof(uint16_t) * 6 * width,
+        address_space_rw(&s->as, dp8393x_crda(s) + sizeof(uint16_t) * 6 * width,
             MEMTXATTRS_UNSPECIFIED, (uint8_t *)data, sizeof(uint16_t), 1);
         s->regs[SONIC_CRDA] = s->regs[SONIC_LLFA];
         s->regs[SONIC_ISR] |= SONIC_ISR_PKTRX;
