diff --git a/src/Model/Estimate.php b/src/Model/Estimate.php
index 23e5b37..af35154 100644
--- a/src/Model/Estimate.php
+++ b/src/Model/Estimate.php
@@ -936,6 +936,14 @@ protected function get_prefix()
      */
     protected function getPrefix(): string
     {
+        $prefix = $this
+            ->dbObject('Prefix')
+            ->getValue();
+
+        if (!empty($prefix)) {
+            return (string)$prefix;
+        }
+
         $config = SiteConfig::current_site_config();
         return (string)$config->EstimateNumberPrefix;
     }
diff --git a/src/Model/Invoice.php b/src/Model/Invoice.php
index 45244d2..9b4504e 100644
--- a/src/Model/Invoice.php
+++ b/src/Model/Invoice.php
@@ -491,6 +491,14 @@ protected function get_prefix()
      */
     protected function getPrefix(): string
     {
+        $prefix = $this
+            ->dbObject('Prefix')
+            ->getValue();
+
+        if (!empty($prefix)) {
+            return (string)$prefix;
+        }
+
         $config = SiteConfig::current_site_config();
         return (string)$config->InvoiceNumberPrefix;
     }