diff --git a/README b/README
index 3f29f3d..54379c4 100644
--- a/README
+++ b/README
@@ -1,6 +1,6 @@
 MinRSS
 ======
-MinRSS (minimal RSS) is an RSS feed reader inspired by suckless.org's
+MinRSS (minimal RSS) is an RSS feed reader for Linux inspired by suckless.org's
 IRC clients ii and sic. Instead of presenting RSS articles as entries
 in a menu, it saves them as files in folders.
 
@@ -12,12 +12,6 @@ rss
   |--post
   `--other_post
 
-Compatibility
--------------
-This program is designed to work on Linux, but it should be possible
-to make it run on other operating systems. If you can do that
-successfully, please contact me about it.
-
 Requirements
 ------------
 You need libcurl and libxml2 to compile MinRSS.
@@ -39,3 +33,13 @@ Using MinRSS
 Make a directory to store your RSS feeds, then cd into it. Then, enter 
 the minrss command to download the RSS feeds. Your feeds will be 
 available as folders in your current working directory.
+
+Compatibility
+-------------
+This program is designed to work on Linux, but it should be possible
+to make it run on other operating systems. If you can do that
+successfully, please contact me about it.
+
+Note that if you use MinRSS on different systems, it will be possible for
+attackers to write malicious filenames, so you should rewrite sanitize()
+accordingly.
diff --git a/util.c b/util.c
index c5cf462..b99c625 100644
--- a/util.c
+++ b/util.c
@@ -54,17 +54,21 @@ san(char *str, int rep)
 	unsigned long long int len = strlen(str);
 	unsigned long long int offset = 0;
 
+	len = len > 255 ? 255 : len;
+
 	char *dup = ecalloc(len + 1, sizeof(char));
 	strcpy(dup, str);
 
 	for (unsigned long long int i = 0; i < len; i++) {
-		if ((dup[i] >= 'a' && dup[i] <= 'z') ||
-			(dup[i] >= 'A' && dup[i] <= 'Z') ||
-			(dup[i] >= '0' && dup[i] <= '9') ||
-			 dup[i] == '-' || dup[i] == '_')
+		char c = dup[i];
+
+		if ((c >= 'a' && c <= 'z') ||
+			(c >= 'A' && c <= 'Z') ||
+			(c >= '0' && c <= '9') ||
+			(c == '.' && i - offset != 0) ||
+			 c == '-' || c == '_' ||
+			 c == ' ')
 			dup[i - offset] = dup[i];
-		else if (dup[i] == ' ')
-			dup[i - offset] = '_';
 		else
 			offset++;
 	}