diff --git a/charts/spire/charts/spire-server/templates/configmap.yaml b/charts/spire/charts/spire-server/templates/configmap.yaml
index 4e22858..0d297c6 100644
--- a/charts/spire/charts/spire-server/templates/configmap.yaml
+++ b/charts/spire/charts/spire-server/templates/configmap.yaml
@@ -298,6 +298,8 @@ plugins:
   {{- end }}
   {{- end }}
 
+{{- $keyManagerUsed = add $keyManagerUsed (len .Values.unsupportedBuiltInPlugins.keyManager) }}
+
 {{- if ne $keyManagerUsed 1 }}
 {{- fail (printf "You have to enable exactly one Key Manager. There are %d enabled." $keyManagerUsed) }}
 {{- end }}