diff --git a/internal/glance/config-fields.go b/internal/glance/config-fields.go
index fd90e2b..0fefb12 100644
--- a/internal/glance/config-fields.go
+++ b/internal/glance/config-fields.go
@@ -117,7 +117,7 @@ func (d *durationField) UnmarshalYAML(node *yaml.Node) error {
 	return nil
 }
 
-var optionalEnvFieldPattern = regexp.MustCompile(`(^|.)\$\{([A-Z_]+)\}`)
+var optionalEnvFieldPattern = regexp.MustCompile(`(^|.)\$\{([A-Z0-9_]+)\}`)
 
 type optionalEnvField string