diff --git a/doc/Makefile b/doc/Makefile
index d4a5c6a6da02687badc92c0e018b9f3f0cdde6d5..27c54c52a28bf173cc2f8fd812712a6f3bef42c5 100644
--- a/doc/Makefile
+++ b/doc/Makefile
@@ -35,7 +35,7 @@ help:
 .PHONY: help clean html web pickle htmlhelp latex changes linkcheck
 
 constants:
-	python make_constants.py > constants.inc
+	python3 make_constants.py > constants.inc
 
 clean:
 	-rm -rf build/*