diff --git a/CMakeLists.txt b/CMakeLists.txt
index fbaf809..087e269 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,6 +1,6 @@
 cmake_minimum_required (VERSION 3.2)
 project(identiconpp
-        VERSION 0.3.6
+        VERSION 0.3.7
         LANGUAGES CXX
 )
 
diff --git a/src/checks.cpp b/src/checks.cpp
index 1ac900e..ed23dc4 100644
--- a/src/checks.cpp
+++ b/src/checks.cpp
@@ -81,6 +81,10 @@ bool Identiconpp::not_hex(const char c)
     {   // a-f
         return false;
     }
+    if (c >= 0x41 && c <= 0x46)
+    {   // A-F
+        return false;
+    }
     if (c >= 0x30 && c <= 0x39)
     {   // 0-9
         return false;