diff --git a/cmd/which-update.rb b/cmd/which-update.rb
index 52935e96..9afd5775 100755
--- a/cmd/which-update.rb
+++ b/cmd/which-update.rb
@@ -20,6 +20,8 @@ def which_update_args
              description: "Update database entries with outdated formula versions."
       switch "--install-missing",
              description: "Install and update formulae that are missing from the database and don't have bottles."
+      switch "--eval-all",
+             description: "Evaluate all installed taps, rather than just the core tap."
       flag   "--max-downloads=",
              description: "Specify a maximum number of formulae to download and update."
       conflicts "--stats", "--commit"
@@ -39,7 +41,8 @@ def which_update
       Homebrew::WhichUpdate.update_and_save! source: args.named.first, commit: args.commit?,
                                              update_existing: args.update_existing?,
                                              install_missing: args.install_missing?,
-                                             max_downloads: args.max_downloads
+                                             max_downloads: args.max_downloads,
+                                             eval_all: args.eval_all?
     end
   end
 end
diff --git a/lib/executables_db.rb b/lib/executables_db.rb
index b92c0dae..464748a2 100644
--- a/lib/executables_db.rb
+++ b/lib/executables_db.rb
@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 require "formula"
+require "formulary"
+require "tap"
 
 module Homebrew
   # ExecutablesDB represents a DB associating formulae to the binaries they
@@ -51,43 +53,50 @@ def changed?
 
     # update the DB with the installed formulae
     # @see #save!
-    def update!(update_existing: false, install_missing: false, max_downloads: nil)
+    def update!(update_existing: false, install_missing: false, max_downloads: nil, eval_all: false)
       downloads = 0
       disabled_formulae = []
-      Formula.all.each do |f|
-        break if max_downloads.present? && downloads > max_downloads.to_i
-        next if f.tap?
 
-        name = f.full_name
-
-        if f.disabled?
-          disabled_formulae << name
-          next
-        end
-
-        update_formula = missing_formula?(f) || (update_existing && outdated_formula?(f))
-
-        # Install unbottled formulae if they should be added/updated
-        if !f.bottled? && install_missing && update_formula
-          downloads += 1
-          ohai "Installing #{f}"
-          system HOMEBREW_BREW_FILE, "install", "--formula", f.to_s
-        end
-
-        # We don't need to worry about updating outdated versions unless update_existing is true
-        if f.latest_version_installed?
-          update_installed_formula f
-        elsif f.bottled? && update_formula
-          downloads += 1
-          update_bottled_formula f
-        end
-
-        # renamed formulae
-        mv f.oldname, name if !f.oldname.nil? && @exes[f.oldname]
-
-        # aliased formulae
-        f.aliases.each do |a|
-          mv a, name if @exes[a]
+      # Evaluate only the core tap by default.
+      taps = eval_all ? Tap.each.to_a : [CoreTap.instance]
+      taps.each do |tap|
+        tap.formula_files_by_name.each do |name, path|
+          f = Formulary.load_formula_from_path(name, path)
+
+          break if max_downloads.present? && downloads > max_downloads.to_i
+          next if f.tap?
+
+          name = f.full_name
+
+          if f.disabled?
+            disabled_formulae << name
+            next
+          end
+
+          update_formula = missing_formula?(f) || (update_existing && outdated_formula?(f))
+
+          # Install unbottled formulae if they should be added/updated
+          if !f.bottled? && install_missing && update_formula
+            downloads += 1
+            ohai "Installing #{f}"
+            system HOMEBREW_BREW_FILE, "install", "--formula", f.to_s
+          end
+
+          # We don't need to worry about updating outdated versions unless update_existing is true
+          if f.latest_version_installed?
+            update_installed_formula f
+          elsif f.bottled? && update_formula
+            downloads += 1
+            update_bottled_formula f
+          end
+
+          # renamed formulae
+          mv f.oldname, name if !f.oldname.nil? && @exes[f.oldname]
+
+          # aliased formulae
+          f.aliases.each do |a|
+            mv a, name if @exes[a]
+          end
         end
       end
 
diff --git a/lib/which_update.rb b/lib/which_update.rb
index e8a6b1ce..23593fbd 100755
--- a/lib/which_update.rb
+++ b/lib/which_update.rb
@@ -45,10 +45,11 @@ def stats(source: nil)
     end
 
     def update_and_save!(source: nil, commit: false, update_existing: false, install_missing: false,
-                         max_downloads: nil)
+                         max_downloads: nil, eval_all: false)
       source ||= default_source
       db = ExecutablesDB.new source
-      db.update!(update_existing: update_existing, install_missing: install_missing, max_downloads: max_downloads)
+      db.update!(update_existing: update_existing, install_missing: install_missing,
+                 max_downloads: max_downloads, eval_all: eval_all)
       db.save!
       return if !commit || !db.changed?