diff --git a/lib/bootboot/bundler_patch.rb b/lib/bootboot/bundler_patch.rb
index f3628c9..5377f20 100644
--- a/lib/bootboot/bundler_patch.rb
+++ b/lib/bootboot/bundler_patch.rb
@@ -21,7 +21,14 @@ def system
       # the Gemfile is different from the Ruby version currently running, we
       # want to write the version specified in `Gemfile` for the current
       # dependency set to the lock file
-      Bundler::Definition.build(Bootboot::GEMFILE, nil, false).ruby_version || super
+      requested_ruby_version = Bundler::Definition.build(Bootboot::GEMFILE, nil, false).ruby_version
+      if requested_ruby_version
+        requirement = Gem::Requirement.new(requested_ruby_version.versions)
+        # unless it's a requirement for an exact ruby version, we can't substitute it
+        # as there's a range of potential versions, so don't override in that case
+        requested_ruby_version = nil unless requirement.exact?
+      end
+      requested_ruby_version || super
     else
       super
     end