diff --git a/stand/libsa/tslog.c b/stand/libsa/tslog.c
index c6164aab02a9..a2791f9dc9c4 100644
--- a/stand/libsa/tslog.c
+++ b/stand/libsa/tslog.c
@@ -1,84 +1,120 @@
 /*-
  * Copyright (c) 2021 Colin Percival
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
 #include <sys/types.h>
 
 #if defined(__amd64__) || defined(__i386__)
 #include <machine/cpufunc.h>
 #elif defined(__aarch64__)
 #include <machine/armreg.h>
 #endif
 
 #include <stand.h>
 
 /* Buffer for holding tslog data in string format. */
 static char * tslog_buf = NULL;
 static size_t tslog_buflen = 0;
 static size_t tslog_bufpos = 0;
 
+static size_t
+tsccat(char * buf, uint64_t tsc)
+{
+	size_t len;
+
+	/* Handle upper digits. */
+	if (tsc >= 10)
+		len = tsccat(buf, tsc / 10);
+	else
+		len = 0;
+
+	/* Write the last digit. */
+	buf[len] = "0123456789"[tsc % 10];
+
+	/* Return the length written. */
+	return (len + 1);
+}
+
 void
 tslog_setbuf(void * buf, size_t len)
 {
 
 	tslog_buf = (char *)buf;
 	tslog_buflen = len;
 	tslog_bufpos = 0;
 }
 
 void
 tslog_getbuf(void ** buf, size_t * len)
 {
 
 	*buf = (void *)tslog_buf;
 	*len = tslog_bufpos;
 }
 
 void
 tslog(const char * type, const char * f, const char * s)
 {
 #if defined(__amd64__) || defined(__i386__)
 	uint64_t tsc = rdtsc();
 #elif defined(__aarch64__)
 	uint64_t tsc = READ_SPECIALREG(cntvct_el0);
 #else
 	uint64_t tsc = 0;
 #endif
-	int len;
 
 	/* If we have no buffer, do nothing. */
 	if (tslog_buf == NULL)
 		return;
 
-	/* Append to existing buffer, if we have enough space. */
-	len = snprintf(&tslog_buf[tslog_bufpos],
-	    tslog_buflen - tslog_bufpos, "0x0 %llu %s %s%s%s\n",
-	    (unsigned long long)tsc, type, f, s ? " " : "", s ? s : "");
-	if ((len > 0) && (tslog_bufpos + len <= tslog_buflen))
-		tslog_bufpos += len;
+	/* Check that we have enough space. */
+	if (tslog_buflen - tslog_bufpos < 32 + strlen(type) + strlen(f) +
+	    (s ? strlen(s) : 0))
+		return;
+
+	/* Append to existing buffer. */
+	strcpy(&tslog_buf[tslog_bufpos], "0x0 ");
+	tslog_bufpos += 4;
+	tslog_bufpos += tsccat(&tslog_buf[tslog_bufpos], tsc);
+	strcpy(&tslog_buf[tslog_bufpos], " ");
+	tslog_bufpos += 1;
+	strcpy(&tslog_buf[tslog_bufpos], type);
+	tslog_bufpos += strlen(type);
+	strcpy(&tslog_buf[tslog_bufpos], " ");
+	tslog_bufpos += 1;
+	strcpy(&tslog_buf[tslog_bufpos], f);
+	tslog_bufpos += strlen(f);
+	if (s != NULL) {
+		strcpy(&tslog_buf[tslog_bufpos], " ");
+		tslog_bufpos += 1;
+		strcpy(&tslog_buf[tslog_bufpos], s);
+		tslog_bufpos += strlen(s);
+	}
+	strcpy(&tslog_buf[tslog_bufpos], "\n");
+	tslog_bufpos += 1;
 }