diff --git a/src/ifcparse/IfcWrite.cpp b/src/ifcparse/IfcWrite.cpp
index 10df36ec54..00b5daf654 100644
--- a/src/ifcparse/IfcWrite.cpp
+++ b/src/ifcparse/IfcWrite.cpp
@@ -98,7 +98,7 @@ class StringBuilderVisitor : public boost::static_visitor<void> {
         std::ostringstream oss;
         oss.imbue(std::locale::classic());
         oss.put('"');
-        oss << std::hex << std::setw(1);
+        oss << std::uppercase << std::hex << std::setw(1);
         unsigned c = (unsigned)b.size();
         unsigned n = (4 - (c % 4)) & 3;
         oss << n;