diff --git a/bin/pkill/pkill.c b/bin/pkill/pkill.c
--- a/bin/pkill/pkill.c
+++ b/bin/pkill/pkill.c
@@ -63,6 +63,7 @@
 #include <errno.h>
 #include <locale.h>
 #include <jail.h>
+#include <sysexits.h>
 
 #define	STATUS_MATCH	0
 #define	STATUS_NOMATCH	1
@@ -130,11 +131,15 @@
 static void	makelist(struct listhead *, enum listtype, char *);
 static int	takepid(const char *, int);
 
+#define	DFLT_BUF_SIZE		_POSIX2_LINE_MAX
+#define	MAX_BUF_INCREMENT	USHRT_MAX	/* Arbitrary */
+
 int
 main(int argc, char **argv)
 {
-	char buf[_POSIX2_LINE_MAX], *mstr, **pargv, *p, *q, *pidfile;
+	char *buf, *mstr, **pargv, *p, *q, *pidfile;
 	const char *execf, *coref;
+	size_t bufsz;
 	int ancestors, debug_opt, did_action;
 	int i, ch, bestidx, rv, criteria, pidfromfile, pidfilelock;
 	size_t jsz;
@@ -146,6 +151,11 @@
 	regmatch_t regmatch;
 	pid_t pid;
 
+	bufsz = DFLT_BUF_SIZE;
+	buf = calloc(1, bufsz);
+	if (buf == NULL)
+		err(EXIT_FAILURE, "calloc");
+
 	setlocale(LC_ALL, "");
 
 	if (strcmp(getprogname(), "pgrep") == 0) {
@@ -346,7 +356,7 @@
 	 */
 	for (; *argv != NULL; argv++) {
 		if ((rv = regcomp(&reg, *argv, cflags)) != 0) {
-			regerror(rv, &reg, buf, sizeof(buf));
+			regerror(rv, &reg, buf, bufsz);
 			errx(STATUS_BADUSAGE,
 			    "Cannot compile regular expression `%s' (%s)",
 			    *argv, buf);
@@ -363,9 +373,26 @@
 			if (matchargs &&
 			    (pargv = kvm_getargv(kd, kp, 0)) != NULL) {
 				jsz = 0;
-				while (jsz < sizeof(buf) && *pargv != NULL) {
+				while (jsz < bufsz && *pargv != NULL) {
+					size_t arglen;
+
+					arglen = strlen(pargv[0]);
+					if (jsz + arglen >= bufsz) {
+						/*
+						 * Grow the buffer to a size
+						 * that hopefully won't require
+						 * further growth.
+						 */
+						bufsz += MAX(MIN(MAX_BUF_INCREMENT,
+						    bufsz), arglen);
+
+						buf = realloc(buf, bufsz);
+						if (buf == NULL)
+							err(1, "realloc");
+					}
+
 					jsz += snprintf(buf + jsz,
-					    sizeof(buf) - jsz,
+					    bufsz - jsz,
 					    pargv[1] != NULL ? "%s " : "%s",
 					    pargv[0]);
 					pargv++;
@@ -384,7 +411,7 @@
 				} else
 					selected[i] = 1;
 			} else if (rv != REG_NOMATCH) {
-				regerror(rv, &reg, buf, sizeof(buf));
+				regerror(rv, &reg, buf, bufsz);
 				errx(STATUS_ERROR,
 				    "Regular expression evaluation error (%s)",
 				    buf);
@@ -576,6 +603,7 @@
 		fprintf(stderr,
 		    "No matching processes belonging to you were found\n");
 
+	free(buf);
 	exit(rv ? STATUS_MATCH : STATUS_NOMATCH);
 }
 
diff --git a/bin/pkill/tests/Makefile b/bin/pkill/tests/Makefile
--- a/bin/pkill/tests/Makefile
+++ b/bin/pkill/tests/Makefile
@@ -2,6 +2,8 @@
 
 .include <bsd.own.mk>
 
+PACKAGE=	tests
+
 TAP_TESTS_SH=			pgrep-F_test
 TAP_TESTS_SH+=			pgrep-LF_test
 TAP_TESTS_SH+=			pgrep-P_test
@@ -10,6 +12,7 @@
 TAP_TESTS_SH+=			pgrep-_s_test
 TAP_TESTS_SH+=			pgrep-g_test
 TAP_TESTS_SH+=			pgrep-i_test
+TAP_TESTS_SH+=			pgrep-f_test
 TAP_TESTS_SH+=			pgrep-j_test
 TEST_METADATA.pgrep-j_test+=	required_user="root"
 TEST_METADATA.pgrep-j_test+=	required_programs="jail jls"
@@ -35,4 +38,6 @@
 TAP_TESTS_SH+=			pkill-t_test
 TAP_TESTS_SH+=			pkill-x_test
 
+${PACKAGE}FILES+=		spin.sh
+
 .include <bsd.test.mk>
diff --git a/bin/pkill/tests/pgrep-f_test.sh b/bin/pkill/tests/pgrep-f_test.sh
new file mode 100644
--- /dev/null
+++ b/bin/pkill/tests/pgrep-f_test.sh
@@ -0,0 +1,50 @@
+#!/bin/sh
+# $FreeBSD$
+
+base=$(dirname $(realpath "$0"))
+
+echo "1..3"
+
+sentinel="findme=test-$$"
+name="pgrep -f"
+spin="sh ${base}/spin.sh"
+
+${spin} ${sentinel} &
+chpid=$!
+sleep 0.3
+pid=$(pgrep -f ${sentinel})
+if [ "$pid" = "$chpid" ]; then
+	echo "ok - $name"
+else
+	echo "not ok - $name"
+fi
+kill $chpid
+
+# This requires growth of the buffer at least one, ideally it will hop
+# immediately from the default size of _POSIX2_LINE_MAX (2048) to
+# _POSIX2_LINE_MAX + ~8192, despite the ususal doubling behavior.
+name="pgrep -f long args"
+longargs=$(jot -b "x" -s "" 8192)
+${spin} ${longargs} ${sentinel} &
+chpid=$!
+sleep 0.3
+pid=$(pgrep -f ${sentinel})
+if [ "$pid" = "$chpid" ]; then
+	echo "ok - $name"
+else
+	echo "not ok - $name"
+fi
+kill $chpid
+
+name="pgrep -f multiple long args"
+longargs=$(jot -b "x" -s "" 8192)
+${spin} ${longargs} ${longargs} ${sentinel} &
+chpid=$!
+sleep 0.3
+pid=$(pgrep -f ${sentinel})
+if [ "$pid" = "$chpid" ]; then
+	echo "ok - $name"
+else
+	echo "not ok - $name"
+fi
+kill $chpid
diff --git a/bin/pkill/tests/spin.sh b/bin/pkill/tests/spin.sh
new file mode 100644
--- /dev/null
+++ b/bin/pkill/tests/spin.sh
@@ -0,0 +1,5 @@
+#!/bin/sh
+
+while true; do
+	sleep 1
+done