diff --git a/rtgui/histogrampanel.cc b/rtgui/histogrampanel.cc
index bbad4ecf3..d7e9bbc69 100644
--- a/rtgui/histogrampanel.cc
+++ b/rtgui/histogrampanel.cc
@@ -29,6 +29,9 @@
 
 using namespace rtengine;
 
+constexpr float HistogramArea::MAX_BRIGHT;
+constexpr float HistogramArea::MIN_BRIGHT;
+
 using ScopeType = Options::ScopeType;
 
 //