Index: src/test/regression.c
===================================================================
--- src/test/regression.c	(revision 989)
+++ src/test/regression.c	(working copy)
@@ -1268,7 +1268,7 @@
       printf("%s\n",icalproperty_as_ical_string(prop));
 
     is("test encoding of 'Timezone\\nwith a newline'",
-       icalproperty_as_ical_string(prop), "DTSTART;VALUE=DATE,TZID=Timezone\\nwith a newline:20090126");
+       icalproperty_as_ical_string(prop), "DTSTART;VALUE=DATE,TZID=Timezone with a newline:20090126\n");
 
     icalproperty_free(prop);
 }
Index: src/libical/icalparameter.c
===================================================================
--- src/libical/icalparameter.c	(revision 989)
+++ src/libical/icalparameter.c	(working copy)
@@ -211,15 +211,86 @@
 	return buf;
 }
 
+/**
+ * checks whether this character is allowed in a (Q)SAFE-CHAR
+ *
+ * QSAFE-CHAR	= WSP / %x21 / %x23-7E / NON-US-ASCII
+ * ; any character except CTLs and DQUOTE
+ * SAFE-CHAR	= WSP / %x21 / %x23-2B / %x2D-39 / %x3C-7E / NON-US-ASCII
+ * ; any character except CTLs, DQUOTE. ";", ":", ","
+ * WSP		= SPACE / HTAB
+ * NON-US-ASCII       = %x80-F8
+ * ; Use restricted by charset parameter
+ * ; on outer MIME object (UTF-8 preferred)
+ */
+int
+icalparameter_is_safe_char(char character, int quoted)
+{
+	if (character == ' ' || character == '\t' || character == '!'
+		|| (character >= 0x80 && character <= 0xF8))
+	{
+		return 1;
+	}
 
+	if (quoted && character >= 0x23 && character <= 0x7e)
+	{
+		return 1;
+	}
+	else if (!quoted && ((character >= 0x23 && character <= 0x2b)
+		|| (character >= 0x2d && character <= 0x39) 
+		|| (character >= 0x3c && character <= 0x7e)))
+	{
+		return 1;
+	}
+
+	return 0;
+}
+
 /**
+ * Appends the parameter text to the buffer, filtering out some characters not
+ * permitted by the specification
+ * 
+ * paramtext	= *SAFE-CHAR
+ * quoted-string= DQUOTE *QSAFE-CHAR DQUOTE
+ */
+void
+icalparameter_append_paramtext(char** buf, char** buf_ptr, size_t* buf_size, const char* param_string)
+{
+	int qm = 0;
+	char* buf_filter = *buf_ptr;
+
+	/* Encapsulate the property in quotes if necessary */
+	if (strpbrk(param_string, ";:,") != 0) {
+		icalmemory_append_char (buf, buf_ptr, buf_size, '"');
+		qm = 1;
+	}
+
+	/* First copy the parameter value */
+        icalmemory_append_string(buf, buf_ptr, buf_size, param_string); 
+
+	/* Then filter the copied data */
+	while (buf_filter < *buf_ptr)
+	{
+		if (! icalparameter_is_safe_char(*buf_filter, qm))
+		{
+			*buf_filter = ' ';
+		}
+		buf_filter++;
+	}
+
+	if (qm == 1) {
+		icalmemory_append_char (buf, buf_ptr, buf_size, '"');
+	}
+}
+
+/**
  * Return a string representation of the parameter according to RFC2445.
  *
  * param	= param-name "=" param-value
  * param-name	= iana-token / x-token
  * param-value	= paramtext /quoted-string
- * paramtext	= *SAFE-SHARE
- * quoted-string= DQUOTE *QSAFE-CHARE DQUOTE
+ * paramtext	= *SAFE-CHAR
+ * quoted-string= DQUOTE *QSAFE-CHAR DQUOTE
  * QSAFE-CHAR	= any character except CTLs and DQUOTE
  * SAFE-CHAR	= any character except CTLs, DQUOTE. ";", ":", ","
  */
@@ -268,17 +339,7 @@
     icalmemory_append_string(&buf, &buf_ptr, &buf_size, "=");
 
     if(param->string !=0){
-        int qm = 0;
-
-	/* Encapsulate the property in quotes if necessary */
-	if (strpbrk(param->string, ";:,") != 0) {
-		icalmemory_append_char (&buf, &buf_ptr, &buf_size, '"');
-		qm = 1;
-	}
-        icalmemory_append_string(&buf, &buf_ptr, &buf_size, param->string); 
-	if (qm == 1) {
-		icalmemory_append_char (&buf, &buf_ptr, &buf_size, '"');
-	}
+        icalparameter_append_paramtext(&buf, &buf_ptr, &buf_size, param->string);
     } else if (param->data != 0){
         const char* str = icalparameter_enum_to_string(param->data);
         icalmemory_append_string(&buf, &buf_ptr, &buf_size, str);