diff --git a/fs/types.go b/fs/types.go
index aed6926b6..7b4267c21 100644
--- a/fs/types.go
+++ b/fs/types.go
@@ -340,7 +340,8 @@ func NewUsageValue[T interface {
 	int64 | uint64 | float64
 }](value T) *int64 {
 	p := new(int64)
-	if value > T(int64(math.MaxInt64)) {
+	// float64(math.MaxInt64) rounds up to 2**63 which doesn't fit in an int64
+	if value >= T(int64(math.MaxInt64)) {
 		*p = math.MaxInt64
 	} else {
 		*p = int64(value)
diff --git a/fs/types_test.go b/fs/types_test.go
new file mode 100644
index 000000000..cd47bfcdb
--- /dev/null
+++ b/fs/types_test.go
@@ -0,0 +1,53 @@
+package fs
+
+import (
+	"math"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewUsageValueInt64(t *testing.T) {
+	for _, test := range []struct {
+		in   int64
+		want int64
+	}{
+		{0, 0},
+		{1 << 60, 1 << 60},
+		{math.MaxInt64, math.MaxInt64},
+	} {
+		assert.Equal(t, test.want, *NewUsageValue(test.in), "in=%d", test.in)
+	}
+}
+
+func TestNewUsageValueUint64(t *testing.T) {
+	for _, test := range []struct {
+		in   uint64
+		want int64
+	}{
+		{0, 0},
+		{math.MaxInt64, math.MaxInt64},
+		{math.MaxInt64 + 1, math.MaxInt64},
+		{math.MaxUint64, math.MaxInt64},
+	} {
+		assert.Equal(t, test.want, *NewUsageValue(test.in), "in=%d", test.in)
+	}
+}
+
+func TestNewUsageValueFloat64(t *testing.T) {
+	// Largest float64 strictly below 2**63 - this still fits in an int64.
+	const belowMax = float64(9223372036854773760)
+	for _, test := range []struct {
+		in   float64
+		want int64
+	}{
+		{0, 0},
+		{1e18, 1000000000000000000}, // Box reports space_amount like this
+		{belowMax, 9223372036854773760},
+		{float64(math.MaxInt64), math.MaxInt64}, // rounds up to 2**63
+		{1e19, math.MaxInt64},
+		{math.Inf(1), math.MaxInt64},
+	} {
+		assert.Equal(t, test.want, *NewUsageValue(test.in), "in=%v", test.in)
+	}
+}