diff --git a/core/fxcrt/fx_number.cpp b/core/fxcrt/fx_number.cpp
index 99e9f41..178ede9 100644
--- a/core/fxcrt/fx_number.cpp
+++ b/core/fxcrt/fx_number.cpp
@@ -50,10 +50,11 @@
     cc++;
   }
 
-  for (; cc < strc.GetLength() && std::isdigit(strc[cc]); ++cc) {
-    // Deliberately not using FXSYS_DecimalCharToInt() in a tight loop to avoid
-    // a duplicate std::isdigit() call.
-    unsigned_val = unsigned_val * 10 + strc[cc] - '0';
+  while (cc < strc.GetLength() && std::isdigit(strc[cc])) {
+    unsigned_val = unsigned_val * 10 + FXSYS_DecimalCharToInt(strc.CharAt(cc));
+    if (!unsigned_val.IsValid())
+      break;
+    cc++;
   }
 
   uint32_t uValue = unsigned_val.ValueOrDefault(0);