diff --git a/src/GBI.cpp b/src/GBI.cpp
index 922e5aa2..f14cdf3c 100644
--- a/src/GBI.cpp
+++ b/src/GBI.cpp
@@ -1,5 +1,6 @@
 #include <algorithm>
 #include <assert.h>
+#include <cctype>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
@@ -206,12 +207,6 @@ void GBIInfo::_makeCurrent(MicrocodeInfo * _pCurrent)
 	m_pCurrent = _pCurrent;
 }
 
-inline
-bool _isDigit(char _c)
-{
-	return _c >= '0' && _c <= '9';
-}
-
 bool GBIInfo::_makeExistingMicrocodeCurrent(u32 uc_start, u32 uc_dstart, u32 uc_dsize)
 {
 	auto iter = std::find_if(m_list.begin(), m_list.end(), [=](const MicrocodeInfo& info) {
@@ -287,7 +282,7 @@ void GBIInfo::loadMicrocode(u32 uc_start, u32 uc_dstart, u16 uc_dsize)
 				}
 				else if (strncmp( &uc_str[14], "L3D", 3 ) == 0) {
 					u32 t = 22;
-					while (!_isDigit(uc_str[t]) && t++ < j);
+					while (!std::isdigit(uc_str[t]) && t++ < j);
 					if (uc_str[t] == '1')
 						type = L3DEX;
 					else if (uc_str[t] == '2')
@@ -295,7 +290,7 @@ void GBIInfo::loadMicrocode(u32 uc_start, u32 uc_dstart, u16 uc_dsize)
 				}
 				else if (strncmp( &uc_str[14], "S2D", 3 ) == 0) {
 					u32 t = 20;
-					while (!_isDigit(uc_str[t]) && t++ < j);
+					while (!std::isdigit(uc_str[t]) && t++ < j);
 					if (uc_str[t] == '1')
 						type = S2DEX;
 					else if (uc_str[t] == '2')