diff --git a/man/remind.1 b/man/remind.1
index 834ee8a8..6edac1ab 100644
--- a/man/remind.1
+++ b/man/remind.1
@@ -2260,7 +2260,9 @@ The maximum number of iterations for the \fBSATISFY\fR clause
 .TP
 .B $MaxStringLen
 A limit on the longest string that \fBRemind\fR will allow you
-to create.  The default is 65535.
+to create.  The default is 65535.  If you set \fB$MaxStringLen\fR to 0
+or to -1, then \fBremind\fR will allow you to create arbitrarily-long
+strings, at least until it runs out of memory.
 .TP
 .B $MinsFromUTC
 The number of minutes between Universal Time Coordinated and local time.  If
@@ -3015,8 +3017,8 @@ not be executed.
 .PP
 If \fImaxlen\fR is specified, then \fBshell()\fR returns the first
 \fImaxlen\fR characters of output (rather than the first 511).  If
-\fImaxlen\fR is specified as a negative number, then \fIall\fR the
-output from \fIcmd\fR is returned.
+\fImaxlen\fR is specified as a negative number, then it defaults to
+the value of the system variable \fB$MaxStringLen\fR.
 .RE
 .TP
 .B shellescape(s_str)
diff --git a/src/expr.c b/src/expr.c
index 766eccc1..483d1d1e 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -828,7 +828,7 @@ static int Add(void)
 	v3.type = STR_TYPE;
 	l1 = strlen(v1.v.str);
 	l2 = strlen(v2.v.str);
-	if (MaxStringLen && (l1 + l2 > (size_t) MaxStringLen)) {
+	if (MaxStringLen > 0 && (l1 + l2 > (size_t) MaxStringLen)) {
 	    DestroyValue(v1); DestroyValue(v2);
 	    return E_STRING_TOO_LONG;
 	}
diff --git a/src/funcs.c b/src/funcs.c
index 9ee89031..c0334b00 100644
--- a/src/funcs.c
+++ b/src/funcs.c
@@ -1572,6 +1572,15 @@ static int FShell(func_info *info)
 	ASSERT_TYPE(1, INT_TYPE);
 	maxlen = ARGV(1);
     }
+
+    /* Don't allow maxlen to exceed the maximum length of
+       a string variable */
+    if (MaxStringLen > 0) {
+        if (maxlen <= 0 || maxlen > MaxStringLen) {
+            maxlen = MaxStringLen;
+        }
+    }
+
     fp = popen(ARGSTR(0), "r");
     if (!fp) return E_IO_ERR;
     while (1) {