diff --git a/client.c b/client.c
index ed4b6b3c7..a99acf682 100644
--- a/client.c
+++ b/client.c
@@ -67,13 +67,14 @@ DO_LUA_EQ(client_t, client, "client")
 static bool
 client_loadprops(client_t * c, screen_t *screen)
 {
+    ssize_t len;
     tag_array_t *tags = &screen->tags;
     char *prop = NULL;
 
-    if(!xutil_gettextprop(globalconf.connection, c->win, _AWESOME_PROPERTIES, &prop))
+    if(!xutil_gettextprop(globalconf.connection, c->win, _AWESOME_PROPERTIES, &prop, &len))
         return false;
 
-    if(a_strlen(prop) != tags->len + 2)
+    if(len != tags->len + 2)
     {
         /* ignore property if the tag count isn't matching */
         p_delete(&prop);
@@ -151,13 +152,14 @@ void
 client_updatetitle(client_t *c)
 {
     char *name;
+    ssize_t len;
 
-    if(!xutil_gettextprop(globalconf.connection, c->win, _NET_WM_NAME, &name))
-        if(!xutil_gettextprop(globalconf.connection, c->win, WM_NAME, &name))
+    if(!xutil_gettextprop(globalconf.connection, c->win, _NET_WM_NAME, &name, &len))
+        if(!xutil_gettextprop(globalconf.connection, c->win, WM_NAME, &name, &len))
             return;
 
     p_delete(&c->name);
-    a_iso2utf8(name, &c->name);
+    a_iso2utf8(&c->name, name, len);
 
     /* call hook */
     luaA_client_userdata_new(globalconf.L, c);
@@ -1311,10 +1313,11 @@ luaA_client_name_get(lua_State *L)
 static int
 luaA_client_name_set(lua_State *L)
 {
+    size_t len;
     client_t **c = luaA_checkudata(L, 1, "client");
-    const char *name = luaL_checkstring(L, 2);
+    const char *name = luaL_checklstring(L, 2, &len);
     p_delete(&(*c)->name);
-    a_iso2utf8(name, &(*c)->name);
+    a_iso2utf8(&(*c)->name, name, len);
     return 0;
 }
 
diff --git a/common/draw.c b/common/draw.c
index c0658d852..00bc4d910 100644
--- a/common/draw.c
+++ b/common/draw.c
@@ -56,18 +56,22 @@ void draw_parser_data_wipe(draw_parser_data_t *pdata)
     draw_image_delete(&pdata->bg_image);
 }
 
-/** Convert text from any charset to UTF-8 using iconv
- * \param iso the ISO string to convert
- * \return NULL if error, otherwise pointer to the new converted string
+/** Convert text from any charset to UTF-8 using iconv.
+ * \param iso The ISO string to convert.
+ * \param len The string size.
+ * \return NULL if error, otherwise pointer to the new converted string.
  */
 char *
-draw_iso2utf8(const char *iso)
+draw_iso2utf8(const char *iso, size_t len)
 {
     iconv_t iso2utf8;
-    size_t len, utf8len;
+    size_t utf8len;
     char *utf8, *utf8p;
 
-    if(!(len = a_strlen(iso)))
+    if(len < 0)
+        len = a_strlen(iso);
+
+    if(!len)
         return NULL;
 
     if(!a_strcmp(nl_langinfo(CODESET), "UTF-8"))
diff --git a/common/draw.h b/common/draw.h
index 7a44388c9..1f7200bd6 100644
--- a/common/draw.h
+++ b/common/draw.h
@@ -142,18 +142,18 @@ draw_context_delete(draw_context_t **ctx)
 font_t *draw_font_new(xcb_connection_t *, int, const char *);
 void draw_font_delete(font_t **);
 
-char * draw_iso2utf8(const char *);
+char * draw_iso2utf8(const char *, size_t);
 
 static inline bool
-a_iso2utf8(const char *str, char **res)
+a_iso2utf8(char **dest, const char *str, ssize_t len)
 {
     char *utf8;
-    if((utf8 = draw_iso2utf8(str)))
+    if((utf8 = draw_iso2utf8(str, len)))
     {
-        *res = utf8;
+        *dest = utf8;
         return true;
     }
-    *res = a_strdup(str);
+    *dest = a_strdup(str);
     return false;
 }
 
diff --git a/common/xutil.c b/common/xutil.c
index 2c017118e..4561deeac 100644
--- a/common/xutil.c
+++ b/common/xutil.c
@@ -32,14 +32,15 @@
 #include "common/atoms.h"
 
 /** Get the string value of an atom.
- * \param conn X connection
- * \param w window
- * \param atom the atom
- * \param text buffer to fill
- * \return true on sucess, falsse on failure
+ * \param conn X connection.
+ * \param w Window.
+ * \param atom The atom.
+ * \param text Buffer to fill.
+ * \param len Length of the filled buffer.
+ * \return True on sucess, false on failure.
  */
 bool
-xutil_gettextprop(xcb_connection_t *conn, xcb_window_t w, xcb_atom_t atom, char **text)
+xutil_gettextprop(xcb_connection_t *conn, xcb_window_t w, xcb_atom_t atom, char **text, ssize_t *len)
 {
     xcb_get_property_cookie_t prop_c;
     xcb_get_property_reply_t *prop_r;
@@ -72,6 +73,7 @@ xutil_gettextprop(xcb_connection_t *conn, xcb_window_t w, xcb_atom_t atom, char
         /* use memcpy() because prop_val may not be \0 terminated */
         memcpy(*text, prop_val, prop_r->value_len);
         (*text)[prop_r->value_len] = '\0';
+        *len = prop_r->value_len;
     }
 
     p_delete(&prop_r);
diff --git a/common/xutil.h b/common/xutil.h
index a0f393b5a..ab72710ea 100644
--- a/common/xutil.h
+++ b/common/xutil.h
@@ -96,7 +96,7 @@ typedef struct
 
 class_hint_t *xutil_get_class_hint(xcb_connection_t *, xcb_window_t);
 
-bool xutil_gettextprop(xcb_connection_t *, xcb_window_t, xcb_atom_t, char **);
+bool xutil_gettextprop(xcb_connection_t *, xcb_window_t, xcb_atom_t, char **, ssize_t *);
 
 void xutil_getlockmask(xcb_connection_t *, xcb_key_symbols_t *,
                        unsigned int *, unsigned int *, unsigned int *);
diff --git a/lua.c b/lua.c
index 52ba678d0..42aa4e79a 100644
--- a/lua.c
+++ b/lua.c
@@ -571,7 +571,7 @@ luaA_parserc(const char* rcfile)
     /* Assure there's at least one tag */
     for(screen = 0; screen < globalconf.screens_info->nscreen; screen++)
         if(!globalconf.screens[screen].tags.len)
-            tag_append_to_screen(tag_new("default", layout_tile, 0.5, 1, 0), screen);
+            tag_append_to_screen(tag_new("default", sizeof("default"), layout_tile, 0.5, 1, 0), screen);
 
     return true;
 }
diff --git a/tag.c b/tag.c
index 3f03a9119..1f8fad29b 100644
--- a/tag.c
+++ b/tag.c
@@ -55,20 +55,21 @@ tag_view(tag_t *tag, bool view)
 }
 
 /** Create a new tag. Parameters values are checked.
- * \param name tag name
- * \param layout layout to use
- * \param mwfact master width factor
- * \param nmaster number of master windows
- * \param ncol number of columns for slaves windows
- * \return a new tag with all these parameters
+ * \param name Tag name.
+ * \param len Tag name length.
+ * \param layout Layout to use.
+ * \param mwfact Master width factor.
+ * \param nmaster Number of master windows.
+ * \param ncol Number of columns for slaves windows.
+ * \return A new tag with all these parameters.
  */
 tag_t *
-tag_new(const char *name, layout_t *layout, double mwfact, int nmaster, int ncol)
+tag_new(const char *name, ssize_t len, layout_t *layout, double mwfact, int nmaster, int ncol)
 {
     tag_t *tag;
 
     tag = p_new(tag_t, 1);
-    a_iso2utf8(name, &tag->name);
+    a_iso2utf8(&tag->name, name, len);
     tag->layout = layout;
 
     /* to avoid error */
@@ -313,6 +314,7 @@ luaA_tag_geti(lua_State *L)
 static int
 luaA_tag_new(lua_State *L)
 {
+    size_t len;
     tag_t *tag;
     int ncol, nmaster;
     const char *name, *lay;
@@ -327,11 +329,11 @@ luaA_tag_new(lua_State *L)
     mwfact = luaA_getopt_number(L, 2, "mwfact", 0.5);
     ncol = luaA_getopt_number(L, 2, "ncol", 1);
     nmaster = luaA_getopt_number(L, 2, "nmaster", 1);
-    lay = luaA_getopt_string(L, 2, "layout", "tile");
+    lay = luaA_getopt_lstring(L, 2, "layout", "tile", &len);
 
     layout = name_func_lookup(lay, LayoutList);
 
-    tag = tag_new(name,
+    tag = tag_new(name, len,
                   layout,
                   mwfact, nmaster, ncol);
 
@@ -443,9 +445,9 @@ luaA_tag_newindex(lua_State *L)
     switch(a_tokenize(attr, len))
     {
       case A_TK_NAME:
-        buf = luaL_checkstring(L, 3);
+        buf = luaL_checklstring(L, 3, &len);
         p_delete(&(*tag)->name);
-        a_iso2utf8(buf, &(*tag)->name);
+        a_iso2utf8(&(*tag)->name, buf, len);
         if((*tag)->screen != TAG_SCREEN_UNDEF)
             widget_invalidate_cache((*tag)->screen, WIDGET_CACHE_TAGS);
         return 0;
diff --git a/tag.h b/tag.h
index 796c94b42..a0c0ed942 100644
--- a/tag.h
+++ b/tag.h
@@ -29,7 +29,7 @@
 #define IS_TILED(client, screen)            (client && !client->isfloating && !client->ismax && client_isvisible(client, screen))
 
 /* Contructor, destructor and referencors */
-tag_t *tag_new(const char *, layout_t *, double, int, int);
+tag_t *tag_new(const char *, ssize_t, layout_t *, double, int, int);
 
 static inline void
 tag_delete(tag_t **tag)
diff --git a/widgets/textbox.c b/widgets/textbox.c
index 006965be7..2a25216ad 100644
--- a/widgets/textbox.c
+++ b/widgets/textbox.c
@@ -136,10 +136,10 @@ luaA_textbox_newindex(lua_State *L)
     switch(a_tokenize(attr, len))
     {
       case A_TK_TEXT:
-        if((buf = luaL_checkstring(L, 3)))
+        if((buf = luaL_checklstring(L, 3, &len)))
         {
             p_delete(&d->text);
-            a_iso2utf8(buf, &d->text);
+            a_iso2utf8(&d->text, buf, len);
         }
         break;
       case A_TK_WIDTH: