Index: kernel/generic/src/lib/str.c
===================================================================
--- kernel/generic/src/lib/str.c	(revision 059a8e4b4f97d287fdb888636dac0f59bfafa019)
+++ kernel/generic/src/lib/str.c	(revision f3378ba994792df869e91f5cc6d510de0e96b03f)
@@ -111,4 +111,11 @@
 #include <debug.h>
 #include <macros.h>
+
+/** Check the condition if wchar_t is signed */
+#ifdef WCHAR_IS_UNSIGNED
+	#define WCHAR_SIGNED_CHECK(cond)  (true)
+#else
+	#define WCHAR_SIGNED_CHECK(cond)  (cond)
+#endif
 
 /** Byte mask consisting of lowest @n bits (out of 8) */
@@ -206,8 +213,8 @@
  *
  * @return EOK if the character was encoded successfully, EOVERFLOW if there
- *	   was not enough space in the output buffer or EINVAL if the character
- *	   code was invalid.
- */
-int chr_encode(wchar_t ch, char *str, size_t *offset, size_t size)
+ *         was not enough space in the output buffer or EINVAL if the character
+ *         code was invalid.
+ */
+int chr_encode(const wchar_t ch, char *str, size_t *offset, size_t size)
 {
 	if (*offset >= size)
@@ -427,5 +434,5 @@
 bool ascii_check(wchar_t ch)
 {
-	if ((ch >= 0) && (ch <= 127))
+	if (WCHAR_SIGNED_CHECK(ch >= 0) && (ch <= 127))
 		return true;
 	
@@ -440,5 +447,5 @@
 bool chr_check(wchar_t ch)
 {
-	if ((ch >= 0) && (ch <= 1114111))
+	if (WCHAR_SIGNED_CHECK(ch >= 0) && (ch <= 1114111))
 		return true;