diff --git a/pgrep.c b/pgrep.c
index 86b7be2d..01563db0 100644
--- a/pgrep.c
+++ b/pgrep.c
@@ -42,8 +42,6 @@
 #define EXIT_FATAL 3
 #define XALLOC_EXIT_CODE EXIT_FATAL
 
-#define CMDSTRSIZE 4096
-
 #include "c.h"
 #include "fileutils.h"
 #include "nsutils.h"
@@ -499,9 +497,10 @@ static struct el * select_procs (int *num)
 	regex_t *preg;
 	pid_t myself = getpid();
 	struct el *list = NULL;
-	char cmdline[CMDSTRSIZE] = "";
-	char cmdsearch[CMDSTRSIZE] = "";
-	char cmdoutput[CMDSTRSIZE] = "";
+        long cmdlen = sysconf(_SC_ARG_MAX) * sizeof(char);
+	char *cmdline = xmalloc(cmdlen);
+	char *cmdsearch = xmalloc(cmdlen);
+	char *cmdoutput = xmalloc(cmdlen);
 	proc_t ns_task;
 
 	ptp = do_openproc();
@@ -563,7 +562,7 @@ static struct el * select_procs (int *num)
 
 		if (task.cmdline && (opt_longlong || opt_full) ) {
 			int i = 0;
-			int bytes = sizeof (cmdline);
+			long bytes = cmdlen;
 			char *str = cmdline;
 
 			/* make sure it is always NUL-terminated */
@@ -586,18 +585,18 @@ static struct el * select_procs (int *num)
 
 		if (opt_long || opt_longlong || (match && opt_pattern)) {
 			if (opt_longlong && task.cmdline)
-				strncpy (cmdoutput, cmdline, sizeof cmdoutput - 1);
+				strncpy (cmdoutput, cmdline, cmdlen - 1);
 			else
-				strncpy (cmdoutput, task.cmd, sizeof cmdoutput - 1);
-			cmdoutput[sizeof cmdoutput - 1] = '\0';
+				strncpy (cmdoutput, task.cmd, cmdlen - 1);
+			cmdoutput[cmdlen - 1] = '\0';
 		}
 
 		if (match && opt_pattern) {
 			if (opt_full && task.cmdline)
-				strncpy (cmdsearch, cmdline, sizeof cmdsearch - 1);
+				strncpy (cmdsearch, cmdline, cmdlen - 1);
 			else
-				strncpy (cmdsearch, task.cmd, sizeof cmdsearch - 1);
-			cmdsearch[sizeof cmdsearch - 1] = '\0';
+				strncpy (cmdsearch, task.cmd, cmdlen - 1);
+			cmdsearch[cmdlen - 1] = '\0';
 
 			if (regexec (preg, cmdsearch, 0, NULL, 0) != 0)
 				match = 0;
@@ -661,6 +660,10 @@ static struct el * select_procs (int *num)
 	closeproc (ptp);
 	*num = matches;
 
+        free(cmdline);
+        free(cmdsearch);
+        free(cmdoutput);
+
 	return list;
 }
 
diff --git a/testsuite/config/unix.exp b/testsuite/config/unix.exp
index bbee2333..61a329ed 100644
--- a/testsuite/config/unix.exp
+++ b/testsuite/config/unix.exp
@@ -118,7 +118,7 @@ proc expect_table_dsc { test match_header match_item } {
 }
 
 proc make_testproc { } {
-    global testproc_path testproc_comm testproc1_pid testproc2_pid topdir
+    global testproc_path testproc_comm testproc_arg_str testproc1_pid testproc2_pid topdir
 
     set testproc_realpath "${topdir}/lib/test_process"
     set testproc_comm "spcorp"
@@ -133,8 +133,19 @@ proc make_testproc { } {
         eof { perror "test proc does not link to test process" }
     }
 
-
-    set testproc1_pid [ exec $testproc_path & ]
+    # make a process with the argument set to a fraction of ARG_MAX length
+    # but small enough we do not run TCL out of memory for regular expressions
+    # nor do we get argument list too long (104857 was found to work on Ubuntu 18.04)
+    set max_arg_len [ expr min([ exec /usr/bin/getconf ARG_MAX ], 104857) ]
+    # ensure we have enough slack to launch the test prog and pgrep
+    set reserved_space [expr max([ string length $testproc_path ], [ string length $topdir ] + 10)]
+    set testproc_arg_str "a"
+    set i $reserved_space
+    while {$i<$max_arg_len} {
+      incr i
+      append testproc_arg_str "a"
+    }
+    set testproc1_pid [ exec $testproc_path $testproc_arg_str & ]
     set testproc2_pid [ exec $testproc_path & ]
 }
 
diff --git a/testsuite/pgrep.test/pgrep.exp b/testsuite/pgrep.test/pgrep.exp
index 9f935e60..c7fae1a4 100644
--- a/testsuite/pgrep.test/pgrep.exp
+++ b/testsuite/pgrep.test/pgrep.exp
@@ -34,9 +34,9 @@ set test "pgrep with : delimiter"
 spawn $pgrep -d : $testproc_comm
 expect_pass "$test" "^${testproc1_pid}:${testproc2_pid}\\s*$"
 
-# FIXME - Need to test against -f flag
 set test "pgrep match against full process name"
-untested $test
+spawn $pgrep -f "$testproc_path\\s+$testproc_arg_str"
+expect_pass "$test" "^$testproc1_pid\\s*$"
 
 set test "pgrep with matching gid"
 spawn $pgrep -G $gid $testproc_comm
@@ -51,8 +51,8 @@ spawn $pgrep -l $testproc_comm
 expect_pass "$test" "^$testproc1_pid\\s+$testproc_comm\\s+$testproc2_pid\\s+$testproc_comm\\s*$"
 
 set test "pgrep with full command line"
-spawn $pgrep -a $testproc_comm
-expect_pass "$test" "^$testproc1_pid\\s+$testproc_path\\s+$testproc2_pid\\s+$testproc_path\\s*$"
+spawn $pgrep -af "$testproc_path$"
+expect_pass "$test" "^$testproc2_pid\\s+$testproc_path\\s*$"
 
 set test "pgrep find newest test pid"
 spawn $pgrep -n $testproc_comm