diff --git a/f90/Makefile.am b/f90/Makefile.am
index ee56177..e9828eb 100644
--- a/f90/Makefile.am
+++ b/f90/Makefile.am
@@ -64,10 +64,12 @@ if UPPER_CASE_MOD
 nodist_include_HEADERS = TYPESIZES.mod NETCDF.mod
 TYPESIZES.mod: typeSizes.o
 NETCDF.mod: $(NETCDF_O)
+BUILT_SOURCES = TYPESIZES.mod
 else
 nodist_include_HEADERS = typesizes.mod netcdf.mod 
 typesizes.mod: typeSizes.o
 netcdf.mod: $(NETCDF_O)
+BUILT_SOURCES = typesizes.mod
 endif
 
 # This is what we are building: a convenience library of F90 functions.