Index: mod_rewrite_helper.php
===================================================================
--- mod_rewrite_helper.php	(revision 15158)
+++ mod_rewrite_helper.php	(working copy)
@@ -79,8 +79,18 @@
 			// domain based primary language
 			$this->primaryLanguageId = $this->Application->siteDomainField('PrimaryLanguageId');
 
+			if (!$this->primaryLanguageId) {
+				// when domain-based language not found -> use site-wide language
+				$this->primaryLanguageId = $this->Application->GetDefaultLanguageId();
+			}
+
 			// domain based primary theme
 			$this->primaryThemeId = $this->Application->siteDomainField('PrimaryThemeId');
+
+			if (!$this->primaryThemeId) {
+				// when domain-based theme not found -> use site-wide theme
+				$this->primaryThemeId = $this->Application->GetDefaultThemeId(true);
+			}
 		}
 
 		function processRewriteURL()