diff --git a/bitset.go b/bitset.go
index bbb75ff..26cd6e4 100644
--- a/bitset.go
+++ b/bitset.go
@@ -1220,7 +1220,7 @@ func (b *BitSet) ShiftLeft(bits uint) {
 	}
 
 	// capacity check
-	if top+bits >= Cap() {
+	if top+bits < bits {
 		panic("You are exceeding the capacity")
 	}
 
@@ -1230,7 +1230,7 @@ func (b *BitSet) ShiftLeft(bits uint) {
 	// not using extendSet() to avoid unneeded data copying
 	nsize := wordsNeeded(top + bits)
 	if len(b.set) < nsize {
-		dst = make([]uint64, nsize, 2*nsize)
+		dst = make([]uint64, nsize)
 	}
 	if top+bits >= b.length {
 		b.length = top + bits + 1