diff --git a/inc/unicode.h b/inc/unicode.h
index 2a31f5a..c7d3318 100644
--- a/inc/unicode.h
+++ b/inc/unicode.h
@@ -9,6 +9,13 @@ typedef uint_least32_t char32_t;
 
 typedef int32_t uchar_t;
 
+#define UNI_EBADCP (-1)
+#define UNI_EULSUR (-2)
+#define UNI_EIBYTE (-3)
+#define UNI_ETBYTE (-4)
+#define UNI_ESTRLN (-5)
+
+
 enum {
     UCHAR_BAD,
     UCHAR_Cc,
@@ -112,23 +119,23 @@ struct uchar_props {
 uchar_props *uni_props   (uchar_t cp);
 int          uni_valid   (uchar_t cp);
 int          uni_classify(uchar_t cp);
-uchar_t      uni_tolower(uchar_t cp);
-uchar_t      uni_toupper(uchar_t cp);
-uchar_t      uni_totitle(uchar_t cp);
+uchar_t      uni_tolower (uchar_t cp);
+uchar_t      uni_toupper (uchar_t cp);
+uchar_t      uni_totitle (uchar_t cp);
 
 int     uni_is_hsur(char16_t cp);
 int     uni_is_lsur(char16_t cp);
 uchar_t uni_surtoc (char16_t hsur, char16_t lsur);
 
-int utf16_chlen(char16_t const *str);
-int utf8_chlen (char     const *str);
+size_t utf16_chlen(char16_t const *str);
+size_t utf8_chlen (char     const *str);
 
-int utf16_dec_s(char16_t const *restrict str, size_t len, uchar_t *restrict ch);
-int utf8_dec_s (char     const *restrict str, size_t len, uchar_t *restrict ch);
-int utf16_dec  (char16_t const *restrict str,             uchar_t *restrict ch);
-int utf8_dec   (char     const *restrict str,             uchar_t *restrict ch);
+size_t utf16_dec_s(char16_t const *restrict str, size_t len, uchar_t *restrict ch);
+size_t utf8_dec_s (char     const *restrict str, size_t len, uchar_t *restrict ch);
+size_t utf16_dec  (char16_t const *restrict str,             uchar_t *restrict ch);
+size_t utf8_dec   (char     const *restrict str,             uchar_t *restrict ch);
 
-int utf16_enc_s(char16_t *str, size_t len, uchar_t ch);
-int utf8_enc_s (char     *str, size_t len, uchar_t ch);
-int utf16_enc  (char16_t *str,             uchar_t ch);
-int utf8_enc   (char     *str,             uchar_t ch);
+size_t utf16_enc_s(char16_t *str, size_t len, uchar_t ch);
+size_t utf8_enc_s (char     *str, size_t len, uchar_t ch);
+size_t utf16_enc  (char16_t *str,             uchar_t ch);
+size_t utf8_enc   (char     *str,             uchar_t ch);
diff --git a/src/code/unicode.c b/src/code/unicode.c
index db2384e..c2008df 100644
--- a/src/code/unicode.c
+++ b/src/code/unicode.c
@@ -49,48 +49,51 @@ uchar_t uni_surtoc(char16_t hsur, char16_t lsur) {
 int utf16_chlen(char16_t const *str) {
     char16_t cp = *str;
     if(uni_is_hsur(cp))      return 2;
-    else if(uni_is_lsur(cp)) return 0;
-    else if(uni_valid(cp))   return 1;
-    return 0;
+    else if(uni_is_lsur(cp)) return UNI_EULSUR;
+    else return 1;
 }
 
-int utf8_chlen(char const *str) {
+size_t utf8_chlen(char const *str) {
     uint8_t byte0 = (uint8_t)*str;
     if(byte0 < 0x80)      return 1;
-    else if(byte0 < 0xc0) return 0; // error
+    else if(byte0 < 0xc0) return UNI_EIBYTE;
     else if(byte0 < 0xe0) return 2;
     else if(byte0 < 0xf0) return 3;
     else if(byte0 < 0xf8) return 4;
-    return 0;
+    return UNI_EIBYTE;
 }
 
-int utf16_dec(char16_t const *restrict str, uchar_t *restrict chp) {
-    int chlen = 0;
+size_t utf16_dec(char16_t const *restrict str, uchar_t *restrict chp) {
+    size_t chlen = 0;
     uchar_t ch;
     if(uni_is_hsur(str[0])) {
         char16_t hsur = str[0];
         char16_t lsur = str[1];
         ch = uni_surtoc(hsur, lsur);
         chlen = 2;
+        if(ch > 0x10ffff) {
+            chlen = UNI_EBADCP;
+            ch = 0xfffd;
+        }
     }
-    else {
+    else(!uni_is_lsur(str[0])) {
         ch = str[0];
     }
-    if(!uni_valid(ch)) {
-        chlen = 0;
+    else {
+        chlen = UNI_EULSUR;
         ch = 0xfffd;
     }
     if(chp != NULL) *chp = ch;
     return chlen;
 }
 
-int utf16_dec_s(
+size_t utf16_dec_s(
     char16_t const *restrict str,
     size_t len,
     uchar_t *restrict chp
 ) {
     if(len == 0) return 0;
-    int chlen;
+    size_t chlen;
     uchar_t ch;
     if(uni_is_hsur(str[0])) {
         if(len < 2) return 0;
@@ -98,33 +101,39 @@ int utf16_dec_s(
         char16_t lsur = str[1];
         ch = uni_surtoc(hsur, lsur);
         chlen = 2;
+        if(ch > 0x10ffff) {
+            chlen = UNI_EBADCP;
+            ch = 0xfffd;
+        }
     }
-    else {
+    else if(!uni_is_lsur(str[0])) {
         ch = str[0];
         chlen = 1;
     }
-    if(!uni_valid(ch)) {
+    else {
+        chlen = UNI_EULSUR;
         ch = 0xfffd;
-        chlen = 0;
     }
     if(chp != NULL) *chp = ch;
     return chlen;
 }
 
-int utf8_dec(char const *restrict str, uchar_t *restrict chp) {
+size_t utf8_dec(char const *restrict str, uchar_t *restrict chp) {
     uint8_t const *ustr = (uint8_t const *)str;
-    int chlen;
+
+    size_t chlen;
     uchar_t ch;
-    if(ustr[0] < 0x80)      chlen = 1, ch = ustr[0];
-    else if(ustr[0] < 0xc0) chlen = 0, ch = 0xfffd;
-    else if(ustr[0] < 0xe0) chlen = 2, ch = ustr[0] & 0x1f;
-    else if(ustr[0] < 0xf0) chlen = 3, ch = ustr[0] & 0x0f;
-    else if(ustr[0] < 0xf8) chlen = 4, ch = ustr[0] & 0x07;
-    else chlen = 0;
-    for(int i = 1; i < chlen; ++i) {
+    if(ustr[0] < 0x80)      ch = ustr[0],        chlen = 1;
+    else if(ustr[0] < 0xc0) ch = 0xfffd,         chlen = UNI_EIBYTE;
+    else if(ustr[0] < 0xe0) ch = ustr[0] & 0x1f, chlen = 2;
+    else if(ustr[0] < 0xf0) ch = ustr[0] & 0x0f, chlen = 3;
+    else if(ustr[0] < 0xf8) ch = ustr[0] & 0x07, chlen = 4;
+    else                    ch = 0xfffd,         chlen = UNI_EIBYTE;
+
+    if(chlen > 0) for(size_t i = 1; i < chlen; ++i) {
         uint8_t trail = ustr[i];
         if((trail & 0xc0) != 0x80) {
-            chlen = 0;
+            chlen = UNI_ETBYTE;
             ch = 0xfffd;
             break;
         }
@@ -132,36 +141,35 @@ int utf8_dec(char const *restrict str, uchar_t *restrict chp) {
         ch |= (trail & 0x3f); 
     }
     if(!uni_valid(ch)) {
-        chlen = 0;
+        chlen = UNI_EBADCP;
         ch = 0xfffd;
     }
     if(chp != NULL) *chp = ch;
     return chlen;
 }
 
-int utf8_dec_s(
+size_t utf8_dec_s(
     char const *restrict str,
     size_t len,
     uchar_t *restrict chp
 ) {
     if(len == 0) return 0;
     uint8_t const *restrict ustr = (uint8_t const *restrict)str;
-    int chlen;
+    size_t chlen;
     uchar_t ch;
-    if(ustr[0] < 0x80)      chlen = 1, ch = ustr[0];
-    else if(ustr[0] < 0xc0) chlen = 0, ch = 0xfffd;
-    else if(ustr[0] < 0xe0) chlen = 2, ch = ustr[0] & 0x1f;
-    else if(ustr[0] < 0xf0) chlen = 3, ch = ustr[0] & 0x0f;
-    else if(ustr[0] < 0xf8) chlen = 4, ch = ustr[0] & 0x07;
-    else chlen = 0;
-    if(len < chlen) {
-        return 0;
+    if(ustr[0] < 0x80)      ch = ustr[0],        chlen = 1;
+    else if(ustr[0] < 0xc0) ch = 0xfffd,         chlen = UNI_EIBYTE;
+    else if(ustr[0] < 0xe0) ch = ustr[0] & 0x1f, chlen = 2;
+    else if(ustr[0] < 0xf0) ch = ustr[0] & 0x0f, chlen = 3;
+    else if(ustr[0] < 0xf8) ch = ustr[0] & 0x07, chlen = 4;
+    else                    ch = 0xfffd,         chlen = UNI_EIBYTE;
+    if(chlen > len) {
+        return UNI_ESTRLN;
     }
-    else chlen = 0;
-    for(int i = 1; i < chlen; ++i) {
+    if(chlen > 0) for(size_t i = 1; i < chlen; ++i) {
         uint8_t trail = ustr[i];
         if((trail & 0xc0) != 0x80) {
-            chlen = 0;
+            chlen = UNI_ETBYTE;
             ch = 0xfffd;
             break;
         }
@@ -169,7 +177,7 @@ int utf8_dec_s(
         ch |= (trail & 0x3f); 
     }
     if(!uni_valid(ch)) {
-        chlen = 0;
+        chlen = UNI_EBADCP;
         ch = 0xfffd;
     }
     if(chp != NULL) *chp = ch;