diff --git a/Library/Homebrew/build.rb b/Library/Homebrew/build.rb
index 98ad387ce2..c63f45f97e 100644
--- a/Library/Homebrew/build.rb
+++ b/Library/Homebrew/build.rb
@@ -114,7 +114,9 @@ class Build
     with_env(new_env) do
       formula.extend(Debrew::Formula) if ARGV.debug?
 
-      formula.brew do |_formula, staging|
+      formula.update_head_version
+
+      formula.brew(fetch: false) do |_formula, staging|
         # For head builds, HOMEBREW_FORMULA_PREFIX should include the commit,
         # which is not known until after the formula has been staged.
         ENV["HOMEBREW_FORMULA_PREFIX"] = formula.prefix
diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index faa86fceec..c33d151c9c 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -1012,11 +1012,11 @@ class Formula
     self.build = Tab.for_formula(self)
 
     new_env = {
-      "TMPDIR"        => HOMEBREW_TEMP,
-      "TEMP"          => HOMEBREW_TEMP,
-      "TMP"           => HOMEBREW_TEMP,
-      "HOMEBREW_PATH" => nil,
-      "PATH"          => ENV["HOMEBREW_PATH"],
+      TMPDIR:        HOMEBREW_TEMP,
+      TEMP:          HOMEBREW_TEMP,
+      TMP:           HOMEBREW_TEMP,
+      HOMEBREW_PATH: nil,
+      PATH:          ENV["HOMEBREW_PATH"],
     }
 
     with_env(new_env) do
@@ -1160,11 +1160,12 @@ class Formula
   # yields |self,staging| with current working directory set to the uncompressed tarball
   # where staging is a Mktemp staging context
   # @private
-  def brew
+  def brew(fetch: true)
     @prefix_returns_versioned_prefix = true
+    active_spec.fetch if fetch
     stage do |staging|
       staging.retain! if Homebrew.args.keep_tmp?
-      prepare_patches
+      fetch_patches if fetch
 
       begin
         yield self, staging
@@ -2078,6 +2079,13 @@ class Formula
     ENV.update(removed)
   end
 
+  def fetch_patches
+    active_spec.add_legacy_patches(patches) if respond_to?(:patches)
+
+    patchlist.grep(DATAPatch) { |p| p.path = path }
+    patchlist.select(&:external?).each(&:fetch)
+  end
+
   private
 
   # Returns the prefix for a given formula version number.
@@ -2147,13 +2155,6 @@ class Formula
     end
   end
 
-  def prepare_patches
-    active_spec.add_legacy_patches(patches) if respond_to?(:patches)
-
-    patchlist.grep(DATAPatch) { |p| p.path = path }
-    patchlist.select(&:external?).each(&:fetch)
-  end
-
   # The methods below define the formula DSL.
   class << self
     include BuildEnvironment::DSL
diff --git a/Library/Homebrew/formula_installer.rb b/Library/Homebrew/formula_installer.rb
index d51ad3780b..dcf57c4d66 100644
--- a/Library/Homebrew/formula_installer.rb
+++ b/Library/Homebrew/formula_installer.rb
@@ -977,6 +977,11 @@ class FormulaInstaller
 
     return if only_deps?
 
+    unless pour_bottle?
+      formula.fetch_patches
+      formula.resources.each(&:fetch)
+    end
+
     downloader.fetch
   end
 
@@ -986,7 +991,7 @@ class FormulaInstaller
     elsif pour_bottle?
       formula.bottle
     else
-      formula.downloader
+      formula
     end
   end
 
diff --git a/Library/Homebrew/patch.rb b/Library/Homebrew/patch.rb
index db49f65e79..1050e5bdf4 100644
--- a/Library/Homebrew/patch.rb
+++ b/Library/Homebrew/patch.rb
@@ -117,8 +117,8 @@ class ExternalPatch
   attr_reader :resource, :strip
 
   def_delegators :resource,
-                 :url, :fetch, :patch_files, :verify_download_integrity, :cached_download,
-                 :clear_cache
+                 :url, :fetch, :patch_files, :verify_download_integrity,
+                 :cached_download, :downloaded?, :clear_cache
 
   def initialize(strip, &block)
     @strip    = strip
diff --git a/Library/Homebrew/resource.rb b/Library/Homebrew/resource.rb
index 1f245fd719..dec25c6de1 100644
--- a/Library/Homebrew/resource.rb
+++ b/Library/Homebrew/resource.rb
@@ -55,6 +55,10 @@ class Resource
     "#{owner.name}--#{escaped_name}"
   end
 
+  def downloaded?
+    cached_download.exist?
+  end
+
   def cached_download
     downloader.cached_location
   end
@@ -68,17 +72,19 @@ class Resource
   # directory. Subclasses that override stage should implement the tmp
   # dir using {Mktemp} so that works with all subtypes.
   def stage(target = nil, &block)
-    raise ArgumentError, "target directory or block is required" unless target || block
+    raise ArgumentError, "target directory or block is required" if target.blank? && block.blank?
 
-    fetch
-    prepare_patches
+    fetch_patches(skip_downloaded: true)
+    fetch unless downloaded?
 
     unpack(target, &block)
   end
 
-  def prepare_patches
+  def fetch_patches(skip_downloaded: false)
     patches.grep(DATAPatch) { |p| p.path = owner.owner.path }
-    patches.select(&:external?).each(&:fetch)
+    patches.select!(&:external?)
+    patches.reject!(&:downloaded?) if skip_downloaded
+    patches.each(&:fetch)
   end
 
   def apply_patches
@@ -115,6 +121,8 @@ class Resource
   def fetch(verify_download_integrity: true)
     HOMEBREW_CACHE.mkpath
 
+    fetch_patches
+
     begin
       downloader.fetch
     rescue ErrorDuringExecution, CurlDownloadStrategyError => e