diff --git a/Library/Homebrew/cmd/install.rb b/Library/Homebrew/cmd/install.rb
index 9e1045e2bd..af41382d3c 100644
--- a/Library/Homebrew/cmd/install.rb
+++ b/Library/Homebrew/cmd/install.rb
@@ -219,7 +219,8 @@ module Homebrew
         end
         opoo msg if msg
       elsif !f.any_version_installed? && old_formula = f.old_installed_formulae.first
-        msg = "#{old_formula.full_name} #{old_formula.installed_version} already installed"
+        installed_version = old_formula.opt_or_installed_prefix_keg.version
+        msg = "#{old_formula.full_name} #{installed_version} already installed"
         if !old_formula.linked? && !old_formula.keg_only?
           msg = <<~EOS
             #{msg}, it's just not linked.
diff --git a/Library/Homebrew/livecheck/livecheck.rb b/Library/Homebrew/livecheck/livecheck.rb
index 6b87804cb0..0ebeaaad7d 100644
--- a/Library/Homebrew/livecheck/livecheck.rb
+++ b/Library/Homebrew/livecheck/livecheck.rb
@@ -80,7 +80,11 @@ module Homebrew
 
         formula.head.downloader.shutup! if formula.head?
 
-        current = formula.head? ? formula.installed_version.version.commit : formula.version
+        current = if formula.head?
+          formula.opt_or_installed_prefix_keg.version.version.commit
+        else
+          formula.version
+        end
 
         latest = if formula.stable?
           version_info = latest_version(formula, args: args)