diff --git a/tools/spi/spidev_test.c b/tools/spi/spidev_test.c
index 61951ed1c908..5bd3159f61a7 100644
--- a/tools/spi/spidev_test.c
+++ b/tools/spi/spidev_test.c
@@ -11,6 +11,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <ctype.h>
 #include <errno.h>
 #include <getopt.h>
 #include <fcntl.h>
@@ -100,28 +101,31 @@ static void hex_dump(const void *src, size_t length, size_t line_size,
  *  Unescape - process hexadecimal escape character
  *      converts shell input "\x23" -> 0x23
  */
-static int unescape(char *_dst, char *_src, size_t len)
+static int unescape(char *src, char *dst, size_t size)
 {
-	int ret = 0;
-	int match;
-	char *src = _src;
-	char *dst = _dst;
+	char *out = dst;
 	unsigned int ch;
 
-	while (*src) {
-		if (*src == '\\' && *(src+1) == 'x') {
-			match = sscanf(src + 2, "%2x", &ch);
-			if (!match)
-				pabort("malformed input string");
+	while (*src && size--) {
+		if (src[0] == '\\' && src[1] != '\0') {
+			src++;
 
-			src += 4;
-			*dst++ = (unsigned char)ch;
-		} else {
-			*dst++ = *src++;
+			if (src[0] == 'x' &&
+			    isxdigit((unsigned char)src[1]) &&
+			    isxdigit((unsigned char)src[2]) &&
+			    sscanf(&src[1], "%2x", &ch)) {
+				*out++ = (unsigned char)ch;
+				src += 3;
+				continue;
+			}
+
+			*out++ = '\\';
+			if (!size--)
+				break;
 		}
-		ret++;
+		*out++ = *src++;
 	}
-	return ret;
+	return out - dst;
 }
 
 static void transfer(int fd, uint8_t const * const tx, uint8_t const * const rx, size_t len)
@@ -455,7 +459,7 @@ static void transfer_escaped_string(int fd, char *str)
 			pabort("can't allocate rx buffer");
 	}
 
-	size = unescape((char *)tx, str, size);
+	size = unescape(str, (char *)tx, size);
 	transfer(fd, tx, rx, size);
 	free(rx);
 	free(tx);