diff --git a/Library/Homebrew/tap.rb b/Library/Homebrew/tap.rb
index 26ed2f11c5730..b55c274fffa11 100644
--- a/Library/Homebrew/tap.rb
+++ b/Library/Homebrew/tap.rb
@@ -1169,7 +1169,8 @@ def formula_files_by_name
       name, formula_hash = item
       # If there's more than one item with the same path: use the longer one to prioritise more specific results.
       existing_path = hash[name]
-      new_path = File.join(tap_path, formula_hash["ruby_source_path"]) # Pathname equivalent is slow in a tight loop
+      # Pathname equivalent is slow in a tight loop
+      new_path = File.join(tap_path, formula_hash.fetch("ruby_source_path"))
       hash[name] = Pathname(new_path) if existing_path.nil? || existing_path.to_s.length < new_path.length
     end
   end
diff --git a/Library/Homebrew/test/formulary_spec.rb b/Library/Homebrew/test/formulary_spec.rb
index 33a0355729cb1..07903bbc4af59 100644
--- a/Library/Homebrew/test/formulary_spec.rb
+++ b/Library/Homebrew/test/formulary_spec.rb
@@ -158,8 +158,6 @@ class Wrong#{described_class.class_s(formula_name)} < Formula
 
     context "with installed Formula" do
       before do
-        allow(described_class).to receive(:loader_for).and_call_original
-
         # don't try to load/fetch gcc/glibc
         allow(DevelopmentTools).to receive_messages(needs_libc_formula?: false, needs_compiler_formula?: false)
       end
@@ -329,6 +327,7 @@ def formula_json_contents(extra_items = {})
               "run_type"    => "immediate",
               "working_dir" => "/$HOME",
             },
+            "ruby_source_path"         => "Formula/#{formula_name}.rb",
           }.merge(extra_items),
         }
       end
@@ -378,7 +377,7 @@ def formula_json_contents(extra_items = {})
       end
 
       before do
-        allow(described_class).to receive(:loader_for).and_return(described_class::FormulaAPILoader.new(formula_name))
+        ENV.delete("HOMEBREW_NO_INSTALL_FROM_API")
 
         # don't try to load/fetch gcc/glibc
         allow(DevelopmentTools).to receive_messages(needs_libc_formula?: false, needs_compiler_formula?: false)