diff --git a/Library/Homebrew/formula_assertions.rb b/Library/Homebrew/formula_assertions.rb
index ed24d9d1b5..12913f36ef 100644
--- a/Library/Homebrew/formula_assertions.rb
+++ b/Library/Homebrew/formula_assertions.rb
@@ -26,7 +26,8 @@ module Homebrew
     # @api public
     sig { params(cmd: T.any(Pathname, String), result: Integer).returns(String) }
     def shell_output(cmd, result = 0)
-      ohai cmd
+      ohai cmd.to_s
+      assert_path_exists cmd, "Pathname '#{cmd}' does not exist!" if cmd.is_a?(Pathname)
       output = `#{cmd}`
       assert_equal result, $CHILD_STATUS.exitstatus
       output
@@ -41,7 +42,8 @@ module Homebrew
     # @api public
     sig { params(cmd: T.any(String, Pathname), input: T.nilable(String), result: T.nilable(Integer)).returns(String) }
     def pipe_output(cmd, input = nil, result = nil)
-      ohai cmd
+      ohai cmd.to_s
+      assert_path_exists cmd, "Pathname '#{cmd}' does not exist!" if cmd.is_a?(Pathname)
       output = IO.popen(cmd, "w+") do |pipe|
         pipe.write(input) unless input.nil?
         pipe.close_write