diff --git a/source/blender/editors/space_outliner/outliner_tree.c b/source/blender/editors/space_outliner/outliner_tree.c
index e3c89c82ec6..e2d43386c5e 100644
--- a/source/blender/editors/space_outliner/outliner_tree.c
+++ b/source/blender/editors/space_outliner/outliner_tree.c
@@ -62,6 +62,7 @@
 
 #include "BLI_blenlib.h"
 #include "BLI_utildefines.h"
+#include "BLI_math.h"
 
 #include "BKE_fcurve.h"
 #include "BKE_main.h"