diff --git a/srfi/srfi-14.h b/srfi/srfi-14.h
index 3989aadcc..cef7e5089 100644
--- a/srfi/srfi-14.h
+++ b/srfi/srfi-14.h
@@ -56,7 +56,7 @@
 
 #define SCM_CHARSET_GET(cs, idx) (((long *) SCM_SMOB_DATA (cs))\
 			           [(idx) / SCM_BITS_PER_LONG] &\
-			 	   (1 << ((idx) % SCM_BITS_PER_LONG)))
+			 	   (1L << ((idx) % SCM_BITS_PER_LONG)))
 
 #define SCM_CHARSETP(x) (!SCM_IMP (x) && (SCM_TYP16 (x) == scm_tc16_charset))