diff --git a/examples/cli/platformio.ini b/examples/cli/platformio.ini
index ff25f1c..e355fcd 100644
--- a/examples/cli/platformio.ini
+++ b/examples/cli/platformio.ini
@@ -20,7 +20,7 @@ default_envs =
 
 [env]
 lib_deps = 
-	libcli@1.3.0
+	libcli@1.4.0
 
 [env:promicro16]
 platform = atmelavr
diff --git a/src/libcli/libcli.cpp b/src/libcli/libcli.cpp
index 6a89dc6..cdfe30b 100644
--- a/src/libcli/libcli.cpp
+++ b/src/libcli/libcli.cpp
@@ -94,28 +94,28 @@ void Cli::readLine(
 }
 
 void Cli::readHex(NumberCallback callback, uintptr_t context, uint32_t limit) {
-    _impl.setCallback(callback, context, limit, 16);
+    _impl.setCallback(callback, context, 16, limit);
 }
 
 void Cli::readHex(NumberCallback callback, uintptr_t context, uint32_t limit, uint32_t defval) {
-    _impl.setCallback(callback, context, limit, defval, 16);
+    _impl.setCallback(callback, context, 16, limit, defval);
 }
 
 void Cli::readDec(NumberCallback callback, uintptr_t context, uint32_t limit) {
-    _impl.setCallback(callback, context, limit, 10);
+    _impl.setCallback(callback, context, 10, limit);
 }
 
 void Cli::readDec(NumberCallback callback, uintptr_t context, uint32_t limit, uint32_t defval) {
-    _impl.setCallback(callback, context, limit, defval, 10);
+    _impl.setCallback(callback, context, 10, limit, defval);
 }
 
 void Cli::readNum(NumberCallback callback, uintptr_t context, uint8_t radix, uint32_t limit) {
-    _impl.setCallback(callback, context, limit, radix);
+    _impl.setCallback(callback, context, radix, limit);
 }
 
 void Cli::readNum(NumberCallback callback, uintptr_t context, uint8_t radix, uint32_t limit,
         uint32_t defval) {
-    _impl.setCallback(callback, context, limit, defval, radix);
+    _impl.setCallback(callback, context, radix, limit, defval);
 }
 
 }  // namespace libcli
diff --git a/src/libcli/libcli_impl.cpp b/src/libcli/libcli_impl.cpp
index 40f6fab..812974d 100644
--- a/src/libcli/libcli_impl.cpp
+++ b/src/libcli/libcli_impl.cpp
@@ -36,8 +36,8 @@ bool isNewline(char c) {
 }
 
 /** Returns number of digits of |number| in |radix|. */
-int8_t getDigits(uint32_t number, uint8_t radix) {
-    int8_t n = 0;
+int_fast8_t getDigits(uint32_t number, uint_fast8_t radix) {
+    int_fast8_t n = 0;
     do {
         n++;
         number /= radix;
@@ -47,23 +47,23 @@ int8_t getDigits(uint32_t number, uint8_t radix) {
 
 }  // namespace
 
-size_t Impl::pad_left(int8_t len, int8_t width, char pad) {
+size_t Impl::pad_left(int_fast8_t len, int_fast8_t width, char pad) {
     size_t size = 0;
     for (auto n = width - len; n > 0; n--)
         size += console->print(pad);
     return size;
 }
 
-size_t Impl::pad_right(int8_t len, int8_t width, char pad) {
+size_t Impl::pad_right(int_fast8_t len, int_fast8_t width, char pad) {
     size_t size = 0;
     for (auto n = width + len; n < 0; n++)
         size += console->print(pad);
     return size;
 }
 
-size_t Impl::printNum(uint32_t number, int8_t width, uint8_t radix, bool newline) {
+size_t Impl::printNum(uint32_t number, int_fast8_t width, uint_fast8_t radix, bool newline) {
     const auto len = getDigits(number, radix);
-    size_t size = pad_left(len, width, radix == 10 ? ' ' : '0');
+    auto size = pad_left(len, width, radix == 10 ? ' ' : '0');
     size += console->print(number, radix);
     size += pad_right(len, width, ' ');
     if (newline)
@@ -71,10 +71,10 @@ size_t Impl::printNum(uint32_t number, int8_t width, uint8_t radix, bool newline
     return size;
 }
 
-size_t Impl::printStr(const __FlashStringHelper *text, int8_t width, bool newline) {
+size_t Impl::printStr(const __FlashStringHelper *text, int_fast8_t width, bool newline) {
     const auto l = strlen_P(reinterpret_cast<const char *>(text));
-    const int8_t len = (l < INT8_MAX) ? l : INT8_MAX;
-    size_t size = pad_left(len, width, ' ');
+    const auto len = (l < INT8_MAX) ? l : INT8_MAX;
+    auto size = pad_left(len, width, ' ');
     size += console->print(text);
     size += pad_right(len, width, ' ');
     if (newline)
@@ -82,10 +82,10 @@ size_t Impl::printStr(const __FlashStringHelper *text, int8_t width, bool newlin
     return size;
 }
 
-size_t Impl::printStr(const char *text, int8_t width, bool newline) {
+size_t Impl::printStr(const char *text, int_fast8_t width, bool newline) {
     const auto l = strlen(text);
-    const int8_t len = (l < INT8_MAX) ? l : INT8_MAX;
-    size_t size = pad_left(len, width, ' ');
+    const auto len = (l < INT8_MAX) ? l : INT8_MAX;
+    auto size = pad_left(len, width, ' ');
     size += console->print(text);
     size += pad_right(len, width, ' ');
     if (newline)
@@ -93,7 +93,7 @@ size_t Impl::printStr(const char *text, int8_t width, bool newline) {
     return size;
 }
 
-size_t Impl::backspace(int8_t n) {
+size_t Impl::backspace(int_fast8_t n) {
     size_t s = 0;
     while (n--)
         s += console->print(F("\b \b"));
@@ -149,7 +149,8 @@ void Impl::processString(char c) {
     }
 }
 
-void Impl::setCallback(NumberCallback callback, uintptr_t context, uint32_t limit, uint8_t radix) {
+void Impl::setCallback(
+        NumberCallback callback, uintptr_t context, uint_fast8_t radix, uint32_t limit) {
     this->callback.number = callback;
     num_width = getDigits(num_limit = limit, num_radix = radix);
     num_value = 0;
@@ -157,8 +158,8 @@ void Impl::setCallback(NumberCallback callback, uintptr_t context, uint32_t limi
     setProcessor(&Impl::processNumber, context);
 }
 
-void Impl::setCallback(NumberCallback callback, uintptr_t context, uint32_t limit, uint32_t defval,
-        uint8_t radix) {
+void Impl::setCallback(NumberCallback callback, uintptr_t context, uint_fast8_t radix,
+        uint32_t limit, uint32_t defval) {
     setCallback(callback, context, limit, radix);
     backspace(num_width);
     num_value = defval;
@@ -166,25 +167,25 @@ void Impl::setCallback(NumberCallback callback, uintptr_t context, uint32_t limi
     printNum(num_value, num_len, radix, false);
 }
 
-bool Impl::checkLimit(char c, uint8_t &n) const {
+bool Impl::checkLimit(char c, uint_fast8_t &n) const {
     if (num_len >= num_width)
         return false;
     c = toUpperCase(c);
-    if (num_radix <= 10 && isDigit(c) && c < num_radix + '0') {
+    if (num_radix <= 10 && c >= '0' && c < num_radix + '0') {
         n = c - '0';
-        const uint32_t limit = num_limit / num_radix;
+        const auto limit = num_limit / num_radix;
         return num_value < limit || (num_value == limit && n <= (num_limit % num_radix));
     }
     if (num_radix == 16 && isHexadecimalDigit(c)) {
         n = isDigit(c) ? c - '0' : c - 'A' + 10;
-        const uint32_t limit = num_limit / 16;
+        const auto limit = num_limit / 16;
         return num_value < limit || (num_value == limit && n <= (num_limit % 16));
     }
     return false;
 }
 
 void Impl::processNumber(char c) {
-    uint8_t n;
+    uint_fast8_t n;
     if (checkLimit(c, n)) {
         num_value *= num_radix;
         num_value += n;
diff --git a/src/libcli/libcli_impl.h b/src/libcli/libcli_impl.h
index 6a0b3cb..d9f931d 100644
--- a/src/libcli/libcli_impl.h
+++ b/src/libcli/libcli_impl.h
@@ -43,17 +43,16 @@ struct Impl final {
     void setCallback(LetterCallback callback, uintptr_t context);
     void setCallback(StringCallback callback, uintptr_t context, char *buffer, size_t size,
             bool hasDefval, bool word);
-    void setCallback(NumberCallback callback, uintptr_t context, uint32_t limit, uint8_t radix);
-    void setCallback(NumberCallback callback, uintptr_t context, uint32_t limit, uint32_t defval,
-            uint8_t radix);
+    void setCallback(NumberCallback callback, uintptr_t context, uint_fast8_t radix, uint32_t limit);
+    void setCallback(NumberCallback callback, uintptr_t context, uint_fast8_t radix, uint32_t limit, uint32_t defval);
 
-    size_t backspace(int8_t n);
-    size_t printNum(uint32_t number, int8_t width, uint8_t radix, bool newline);
-    size_t printStr(const __FlashStringHelper *str, int8_t width, bool newline);
-    size_t printStr(const char *str, int8_t width, bool newline);
+    size_t backspace(int_fast8_t n);
+    size_t printNum(uint32_t number, int_fast8_t width, uint_fast8_t radix, bool newline);
+    size_t printStr(const __FlashStringHelper *str, int_fast8_t width, bool newline);
+    size_t printStr(const char *str, int_fast8_t width, bool newline);
 
     /** Delegate methods for Print. */
-    size_t write(uint8_t val) { return console->write(val); }
+    size_t write(uint_fast8_t val) { return console->write(val); }
     size_t write(const uint8_t *buf, size_t size) { return console->write(buf, size); }
     int availableForWrite() { return console->availableForWrite(); }
 
@@ -93,9 +92,9 @@ struct Impl final {
     void processLetter(char c);
     void processString(char c);
     void processNumber(char c);
-    bool checkLimit(char c, uint8_t &n) const;
-    size_t pad_left(int8_t len, int8_t width, char pad);
-    size_t pad_right(int8_t len, int8_t width, char pad);
+    bool checkLimit(char c, uint_fast8_t &n) const;
+    size_t pad_left(int_fast8_t len, int_fast8_t width, char pad);
+    size_t pad_right(int_fast8_t len, int_fast8_t width, char pad);
 
     /** No copy constructor. */
     Impl(Impl const &) = delete;