diff --git a/src/indent.c b/src/indent.c
index cd03f25..51af4df 100644
--- a/src/indent.c
+++ b/src/indent.c
@@ -70,9 +70,12 @@
     {
 	int n = atoi((char *)cp);
 
+	// Catch negative values, overflow and ridiculous big values.
 	if (n < 0 || n > 9999)
 	{
 	    semsg(_(e_invarg2), cp);
+	    vim_free(*array);
+	    *array = NULL;
 	    return FAIL;
 	}
 	(*array)[t++] = n;
@@ -1615,12 +1618,18 @@
     else
 	new_ts_str = vim_strnsave(new_ts_str, eap->arg - new_ts_str);
 #else
-    new_ts = getdigits(&(eap->arg));
-    if (new_ts < 0)
+    ptr = eap->arg;
+    new_ts = getdigits(&ptr);
+    if (new_ts < 0 && *eap->arg == '-')
     {
 	emsg(_(e_positive));
 	return;
     }
+    if (new_ts < 0 || new_ts > 9999)
+    {
+	semsg(_(e_invarg2), eap->arg);
+	return;
+    }
     if (new_ts == 0)
 	new_ts = curbuf->b_p_ts;
 #endif