diff --git a/programmer.h b/programmer.h
index b10f568..c36b452 100644
--- a/programmer.h
+++ b/programmer.h
@@ -661,6 +661,7 @@
 int serialport_shutdown(void *data);
 int serialport_write(unsigned char *buf, unsigned int writecnt);
 int serialport_read(unsigned char *buf, unsigned int readcnt);
+int serialport_read_nonblock(unsigned char *c, unsigned int readcnt, unsigned int timeout, unsigned int *really_read);
 
 /* Serial port/pin mapping:
 
diff --git a/serial.c b/serial.c
index 9a759ae..d1e2cea 100644
--- a/serial.c
+++ b/serial.c
@@ -361,3 +361,73 @@
 
 	return 0;
 }
+
+/* Tries up to timeout ms to read readcnt characters and places them into the array starting at c. Returns
+ * 0 on success, positive values on temporary errors (e.g. timeouts) and negative ones on permanent errors.
+ * If really_read is not NULL, this function sets its contents to the number of bytes read successfully. */
+int serialport_read_nonblock(unsigned char *c, unsigned int readcnt, unsigned int timeout, unsigned int *really_read)
+{
+	int ret = 1;
+	/* disable blocked i/o and declare platform-specific variables */
+#ifdef _WIN32
+	DWORD rv;
+	COMMTIMEOUTS oldTimeout;
+	COMMTIMEOUTS newTimeout = {
+		.ReadIntervalTimeout = MAXDWORD,
+		.ReadTotalTimeoutMultiplier = 0,
+		.ReadTotalTimeoutConstant = 0,
+		.WriteTotalTimeoutMultiplier = 0,
+		.WriteTotalTimeoutConstant = 0
+	};
+	if(!GetCommTimeouts(sp_fd, &oldTimeout)) {
+		msg_perr_strerror("Could not get serial port timeout settings: ");
+		return -1;
+	}
+	if(!SetCommTimeouts(sp_fd, &newTimeout)) {
+#else
+	ssize_t rv;
+	const int flags = fcntl(sp_fd, F_GETFL);
+	if (fcntl(sp_fd, F_SETFL, flags | O_NONBLOCK) != 0) {
+#endif
+		msg_perr_strerror("Could not set serial port timeout settings %s");
+		return -1;
+	}
+
+	int i;
+	int rd_bytes = 0;
+	for (i = 0; i < timeout; i++) {
+		msg_pspew("readcnt %d rd_bytes %d\n", readcnt, rd_bytes);
+#ifdef _WIN32
+		ReadFile(sp_fd, c + rd_bytes, readcnt - rd_bytes, &rv, NULL);
+		msg_pspew("read %lu bytes\n", rv);
+#else
+		rv = read(sp_fd, c + rd_bytes, readcnt - rd_bytes);
+		msg_pspew("read %zd bytes\n", rv);
+#endif
+		if ((rv == -1) && (errno != EAGAIN)) {
+			msg_perr_strerror("Serial port read error: ");
+			ret = -1;
+			break;
+		}
+		if (rv > 0)
+			rd_bytes += rv;
+		if (rd_bytes == readcnt) {
+			ret = 0;
+			break;
+		}
+		internal_delay(1000);	/* 1ms units */
+	}
+	if (really_read != NULL)
+		*really_read = rd_bytes;
+
+	/* restore original blocking behavior */
+#ifdef _WIN32
+	if (!SetCommTimeouts(sp_fd, &oldTimeout)) {
+#else
+	if (fcntl(sp_fd, F_SETFL, flags) != 0) {
+#endif
+		msg_perr_strerror("Could not restore serial port timeout settings: %s\n");
+		ret = -1;
+	}
+	return ret;
+}
diff --git a/serprog.c b/serprog.c
index c36c93d..15d1d1b 100644
--- a/serprog.c
+++ b/serprog.c
@@ -115,26 +115,6 @@
 	return sock;
 }
 
-/* Returns 0 on success and places the character read into the location pointed to by c.
- * Returns positive values on temporary errors and negative ones on permanent errors.
- * An iteration of one loop takes up to 1ms. */
-static int sp_sync_read_timeout(unsigned int loops, unsigned char *c)
-{
-	int i;
-	for (i = 0; i < loops; i++) {
-		ssize_t rv;
-		rv = read(sp_fd, c, 1);
-		if (rv == 1)
-			return 0;
-		if ((rv == -1) && (errno != EAGAIN)) {
-			msg_perr("read: %s\n", strerror(errno));
-			return -1;
-		}
-		usleep(1000);	/* 1ms units */
-	}
-	return 1;
-}
-
 /* Synchronize: a bit tricky algorithm that tries to (and in my tests has *
  * always succeeded in) bring the serial protocol to known waiting-for-   *
  * command state - uses nonblocking read - rest of the driver uses	  *
@@ -174,12 +154,12 @@
 		msg_pdbg(".");
 		fflush(stdout);
 		for (n = 0; n < 10; n++) {
-			int ret = sp_sync_read_timeout(50, &c);
+			int ret = serialport_read_nonblock(&c, 1, 50, NULL);
 			if (ret < 0)
 				goto err_out;
 			if (ret > 0 || c != S_NAK)
 				continue;
-			ret = sp_sync_read_timeout(20, &c);
+			ret = serialport_read_nonblock(&c, 1, 20, NULL);
 			if (ret < 0)
 				goto err_out;
 			if (ret > 0 || c != S_ACK)
@@ -189,12 +169,12 @@
 				msg_perr("sync write: %s\n", strerror(errno));
 				return 1;
 			}
-			ret = sp_sync_read_timeout(500, &c);
+			ret = serialport_read_nonblock(&c, 1, 500, NULL);
 			if (ret < 0)
 				goto err_out;
 			if (ret > 0 || c != S_NAK)
 				break;	/* fail */
-			ret = sp_sync_read_timeout(100, &c);
+			ret = serialport_read_nonblock(&c, 1, 100, NULL);
 			if (ret > 0 || ret < 0)
 				goto err_out;
 			if (c != S_ACK)