diff --git a/rtengine/canon_cr3_decoder.cc b/rtengine/canon_cr3_decoder.cc
index a64a83010..8b39c3b02 100644
--- a/rtengine/canon_cr3_decoder.cc
+++ b/rtengine/canon_cr3_decoder.cc
@@ -59,6 +59,8 @@
 
 #include "dcraw.h"
 
+#include "rt_math.h"
+
 void DCraw::parse_canon_cr3()
 {
     strncpy(make, "Canon", sizeof(make));