diff --git a/ext/bio/twobit/twobit.c b/ext/bio/twobit/twobit.c
index f875217..ce197e0 100644
--- a/ext/bio/twobit/twobit.c
+++ b/ext/bio/twobit/twobit.c
@@ -250,8 +250,8 @@ twobit_sequence(VALUE self, VALUE chrom, VALUE rbstart, VALUE rbend)
 	TwoBit *tb;
 
 	ch = StringValueCStr(chrom);
-	startl = NUM2UINT32(rbstart);
-	endl = NUM2UINT32(rbend);
+	startl = NUM2ULONG(rbstart);
+	endl = NUM2ULONG(rbend);
 	tb = getTwoBit(self);
 
 	if (!tb)