diff --git a/ruby.yaml b/ruby.yaml
index 3f83716..626331b 100644
--- a/ruby.yaml
+++ b/ruby.yaml
@@ -30,7 +30,8 @@ data:
                 # From ruby.spec Summary
                 rationale: An interpreter of object-oriented scripting language
                 buildorder: 101
-                ref: master
+                # Set a reference on master to guarantee the Ruby version 2.5.
+                ref: ecbc53b
             rubygem-abrt:
                 # From rubygem-abrt.spec Summary
                 rationale: >-