diff --git a/libkmipclient/utils.c b/libkmipclient/utils.c
index 0baf586c..fcbeeec7 100644
--- a/libkmipclient/utils.c
+++ b/libkmipclient/utils.c
@@ -166,13 +166,16 @@ int kmip_parse_hex(const char *str, bool has_prefix, unsigned char **val,
  * Format a hex string from the byte array specified in val. The caller must
  * free the returned str.
  */
-int kmip_format_hex(const unsigned char *val, uint32_t length, bool prefix,
+int kmip_format_hex(const unsigned char *val, size_t length, bool prefix,
 		    char **str)
 {
-	uint32_t str_len, i;
+	size_t str_len, i;
 	char tmp[4];
 	char *ret;
 
+	if (length > (SIZE_MAX - ((prefix ? 2 : 0) + 1)) / 2)
+		return -EINVAL;
+
 	str_len = length * 2 + (prefix ? 2 : 0) + 1;
 	ret = calloc(1, str_len);
 	if (ret == NULL)
diff --git a/libkmipclient/utils.h b/libkmipclient/utils.h
index a8ef8c5c..8728fbe3 100644
--- a/libkmipclient/utils.h
+++ b/libkmipclient/utils.h
@@ -38,7 +38,7 @@ int kmip_parse_decimal_uint(const char *str, uint64_t *val);
 int kmip_parse_hex_int(const char *str, int64_t *val);
 int kmip_parse_hex(const char *str, bool has_prefix, unsigned char **val,
 		   uint32_t *length);
-int kmip_format_hex(const unsigned char *val, uint32_t length, bool prefix,
+int kmip_format_hex(const unsigned char *val, size_t length, bool prefix,
 		    char **str);
 
 int kmip_parse_bignum(const char *str, bool has_prefix, BIGNUM **bn);