diff --git a/ext/f2c_libs/arith.h b/ext/f2c_libs/arith.h
index 76539f82b..995e5b254 100644
--- a/ext/f2c_libs/arith.h
+++ b/ext/f2c_libs/arith.h
@@ -1,2 +1,3 @@
 #define IEEE_8087
 #define Arith_Kind_ASL 1
+#define Double_Align