diff --git a/docs/metrics/extend/customresourcestate-metrics.md b/docs/metrics/extend/customresourcestate-metrics.md
index c28b04b0f..431fd0f1b 100644
--- a/docs/metrics/extend/customresourcestate-metrics.md
+++ b/docs/metrics/extend/customresourcestate-metrics.md
@@ -337,7 +337,8 @@ Supported types are:
 * `nil` is generally mapped to `0.0` if NilIsZero is `true`, otherwise it will throw an error
 * for bool `true` is mapped to `1.0` and `false` is mapped to `0.0`
 * for string the following logic applies
-  * `"true"` and `"yes"` are mapped to `1.0`, `"false"`, `"no"` and `"unknown"` are mapped to `0.0` (all case-insensitive)
+  * `"true"` and `"yes"` are mapped to `1.0`, `"false"` and `"no"` are mapped to `0.0` (all case-insensitive)
+  * `"unknown"` is mapped to `-1.0` (all case-insensitive)
   * RFC3339 times are parsed to float timestamp  
   * Quantities like "250m" or "512Gi" are parsed to float using <https://github.com/kubernetes/apimachinery/blob/master/pkg/api/resource/quantity.go>
   * Percentages ending with a "%" are parsed to float
diff --git a/pkg/customresourcestate/registry_factory.go b/pkg/customresourcestate/registry_factory.go
index 39c261bd2..26639e81a 100644
--- a/pkg/customresourcestate/registry_factory.go
+++ b/pkg/customresourcestate/registry_factory.go
@@ -727,7 +727,7 @@ func toFloat64(value interface{}, nilIsZero bool) (float64, error) {
 		}
 		return 0, nil
 	case string:
-		// The string contains a boolean as a string
+		// The string is a boolean or `"unknown"` according to https://pkg.go.dev/k8s.io/apimachinery/pkg/apis/meta/v1#Condition
 		normalized := strings.ToLower(value.(string))
 		if normalized == "true" || normalized == "yes" {
 			return 1, nil
@@ -736,7 +736,7 @@ func toFloat64(value interface{}, nilIsZero bool) (float64, error) {
 			return 0, nil
 		}
 		if normalized == "unknown" {
-			return 0, nil
+			return -1, nil
 		}
 		// The string contains a RFC3339 timestamp
 		if t, e := time.Parse(time.RFC3339, value.(string)); e == nil {