diff --git a/Library/Homebrew/cmd/untap.rb b/Library/Homebrew/cmd/untap.rb
index 3c51d60dfa..5245f4ad78 100644
--- a/Library/Homebrew/cmd/untap.rb
+++ b/Library/Homebrew/cmd/untap.rb
@@ -27,21 +27,23 @@ module Homebrew
     args.named.to_installed_taps.each do |tap|
       odie "Untapping #{tap} is not allowed" if tap.core_tap? && !Homebrew::EnvConfig.install_from_api?
 
-      installed_tap_formulae = Formula.installed.select { |formula| formula.tap == tap }
-      installed_tap_casks = Cask::Caskroom.casks.select { |cask| cask.tap == tap }
+      if !Homebrew::EnvConfig.install_from_api? || (!tap.core_tap? && tap != "homebrew/cask")
+        installed_tap_formulae = Formula.installed.select { |formula| formula.tap == tap }
+        installed_tap_casks = Cask::Caskroom.casks.select { |cask| cask.tap == tap }
 
-      if installed_tap_formulae.present? || installed_tap_casks.present?
-        installed_names = (installed_tap_formulae + installed_tap_casks.map(&:token)).join("\n")
-        if args.force? || Homebrew::EnvConfig.developer?
-          opoo <<~EOS
-            Untapping #{tap} even though it contains the following installed formulae or casks:
-            #{installed_names}
-          EOS
-        else
-          odie <<~EOS
-            Refusing to untap #{tap} because it contains the following installed formulae or casks:
-            #{installed_names}
-          EOS
+        if installed_tap_formulae.present? || installed_tap_casks.present?
+          installed_names = (installed_tap_formulae + installed_tap_casks.map(&:token)).join("\n")
+          if args.force? || Homebrew::EnvConfig.developer?
+            opoo <<~EOS
+              Untapping #{tap} even though it contains the following installed formulae or casks:
+              #{installed_names}
+            EOS
+          else
+            odie <<~EOS
+              Refusing to untap #{tap} because it contains the following installed formulae or casks:
+              #{installed_names}
+            EOS
+          end
         end
       end