diff --git a/autotest/HexAtoi/Etalon.log b/autotest/HexAtoi/Etalon.log
new file mode 100644
index 000000000..55016f910
--- /dev/null
+++ b/autotest/HexAtoi/Etalon.log
@@ -0,0 +1,27 @@
+* C:\upp\out\autotest\CLANGx64.Debug.Debug_Full\HexAtoi.exe 22.05.2023 09:24:04, user: cxl
+
+s = 1;
+CParser(s).ReadNumber(2) = 1
+CParser(s).ReadNumber(8) = 1
+CParser(s).ReadNumber(10) = 1
+CParser(s).ReadNumber(16) = 1
+s = 9;
+CParser(s).ReadNumber(2) = Error
+CParser(s).ReadNumber(8) = Error
+CParser(s).ReadNumber(10) = 9
+CParser(s).ReadNumber(16) = 9
+s = a;
+CParser(s).ReadNumber(2) = Error
+CParser(s).ReadNumber(8) = Error
+CParser(s).ReadNumber(10) = Error
+CParser(s).ReadNumber(16) = 10
+s = f;
+CParser(s).ReadNumber(2) = Error
+CParser(s).ReadNumber(8) = Error
+CParser(s).ReadNumber(10) = Error
+CParser(s).ReadNumber(16) = 15
+s = a0;
+CParser(s).ReadNumber(2) = Error
+CParser(s).ReadNumber(8) = Error
+CParser(s).ReadNumber(10) = Error
+CParser(s).ReadNumber(16) = 160
diff --git a/autotest/HexAtoi/HexAtoi.cpp b/autotest/HexAtoi/HexAtoi.cpp
new file mode 100644
index 000000000..439884b8c
--- /dev/null
+++ b/autotest/HexAtoi/HexAtoi.cpp
@@ -0,0 +1,18 @@
+#include <Core/Core.h>
+
+using namespace Upp;
+
+CONSOLE_APP_MAIN
+{
+	StdLogSetup(LOG_COUT|LOG_FILE);
+
+	for(String s : { "1;", "9;", "a;", "f;", "a0;" }) {
+		DDUMP(s);
+		try { DDUMP(CParser(s).ReadNumber(2)); } catch(CParser::Error) { LOG("Error"); }
+		try { DDUMP(CParser(s).ReadNumber(8)); } catch(CParser::Error) { LOG("Error"); }
+		try { DDUMP(CParser(s).ReadNumber(10)); } catch(CParser::Error) { LOG("Error"); }
+		try { DDUMP(CParser(s).ReadNumber(16)); } catch(CParser::Error) { LOG("Error"); }
+	}
+	
+	CheckLogEtalon();
+}
diff --git a/autotest/HexAtoi/HexAtoi.upp b/autotest/HexAtoi/HexAtoi.upp
new file mode 100644
index 000000000..520b3d554
--- /dev/null
+++ b/autotest/HexAtoi/HexAtoi.upp
@@ -0,0 +1,10 @@
+uses
+	Core;
+
+file
+	Etalon.log,
+	HexAtoi.cpp;
+
+mainconfig
+	"" = "";
+
diff --git a/uppsrc/Core/Convert.hpp b/uppsrc/Core/Convert.hpp
index ba294a72e..13687d16e 100644
--- a/uppsrc/Core/Convert.hpp
+++ b/uppsrc/Core/Convert.hpp
@@ -29,9 +29,11 @@ const CHAR *ScanUint0(UINT& result, const CHAR *s, bool& overflow)
 		if(base > 10) {
 			if(c <= '9')
 				return c - '0';
-			if(c <= 'Z')
+			if(c >= 'A' && c <= 'Z')
 				return c - 'A' + 10;
-			return c - 'a' + 10;
+			if(c >= 'a' && c <= 'z')
+				return c - 'a' + 10;
+			return -1;
 		}
 		return c - '0';
 	};