diff --git a/source/f90/Makefile b/source/f90/Makefile
index 3a8a62b0e6bf693444b6bebb22d01e94991324bc..26057a7604c7b2f3f689d3610a29b37923b33af0 100644
--- a/source/f90/Makefile
+++ b/source/f90/Makefile
@@ -12,6 +12,9 @@ ifeq "$(GFORTAN_VERSION_GE_5)" "1"
 	FFLAGS += -fdiagnostics-color=auto
 endif
 
+# python3 interpreter
+PYTHON3 = python3
+
 # implicit rules for compiling fortran files
 %.o:       %.f90 ; $(FC) $(FFLAGS) -c $< 
 %_mod.mod: %.f90 ; $(FC) $(FFLAGS) -c $<