diff --git a/src/common/uri.cpp b/src/common/uri.cpp
index 60a2128679..ff01b850f5 100644
--- a/src/common/uri.cpp
+++ b/src/common/uri.cpp
@@ -90,9 +90,9 @@ void wxURI::Clear()
 /* static */
 int wxURI::CharToHex(char c)
 {
-    if ((c >= 'A') && (c <= 'Z'))
+    if ((c >= 'A') && (c <= 'F'))
         return c - 'A' + 10;
-    if ((c >= 'a') && (c <= 'z'))
+    if ((c >= 'a') && (c <= 'f'))
         return c - 'a' + 10;
     if ((c >= '0') && (c <= '9'))
         return c - '0';