diff --git a/lib/linguist/languages.yml b/lib/linguist/languages.yml
index 4f9c8b8d..37557796 100644
--- a/lib/linguist/languages.yml
+++ b/lib/linguist/languages.yml
@@ -932,6 +932,7 @@ PowerShell:
 Prolog:
   type: programming
   color: "#74283c"
+  primary_extension: .prolog
   extensions:
   - .pl
   - .pro