diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8c5eeae..4d18e2e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -24,7 +24,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v2
         with:
-          go-version: '~1.16.6'
+          go-version: '~1.17.9'
         id: go
 
       - name: Install utilities
diff --git a/uint32_store.go b/uint32_store.go
index a909d6b..81f150c 100644
--- a/uint32_store.go
+++ b/uint32_store.go
@@ -114,10 +114,13 @@ func (b *uint32Builder) alloc(nByteValues byte) []byteValue {
 		*cur = (*cur)[: curLen+n : curCap]
 		return (*cur)[curLen:]
 	}
-	newCap := curCap
-	if newCap < maxBuildBufSize {
+	newCap := curCap * 2
+	for newCap < n {
 		newCap *= 2
 	}
+	if newCap > maxBuildBufSize {
+		newCap = maxBuildBufSize
+	}
 	a := make([]byteValue, n, newCap)
 	b.all = append(b.all, a)
 	return a
diff --git a/uint32_store_test.go b/uint32_store_test.go
index 7ce8942..579eb9c 100644
--- a/uint32_store_test.go
+++ b/uint32_store_test.go
@@ -14,22 +14,22 @@ import (
 )
 
 func TestFastStringToUint32Empty(t *testing.T) {
-	ms := mapSliceN(nil, 0)
-	fm := faststringmap.NewUint32Store(ms)
-	if keys := ms.AppendKeys(nil); len(keys) != 0 {
-		t.Errorf("keys should be empty, got %#v", keys)
-	}
-	for _, k := range []string{"", "a", "foo", "ß"} {
-		if actV, ok := fm.LookupString(k); ok {
-			t.Errorf("%q present when not expected, got %d", k, actV)
-		}
-	}
+	ms := mapSliceN(map[string]uint32{"": 1, "a": 2, "foo": 3, "ß": 4}, 0)
+	checkWithMapSlice(t, ms)
+}
+
+func TestFastStringToUint32BigSpan(t *testing.T) {
+	ms := mapSliceN(map[string]uint32{"a!": 1, "a~": 2}, 2)
+	checkWithMapSlice(t, ms)
 }
 
 func TestFastStringToUint32(t *testing.T) {
 	const nStrs = 8192
 	m := randomSmallStrings(nStrs, 8)
-	ms := mapSliceN(m, len(m)/2)
+	checkWithMapSlice(t, mapSliceN(m, len(m)/2))
+}
+
+func checkWithMapSlice(t *testing.T, ms mapSlice) {
 	fm := faststringmap.NewUint32Store(ms)
 
 	for _, k := range ms.in {