diff --git a/CHANGES.md b/CHANGES.md
index 1257adc..588e1f9 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -3,6 +3,7 @@
 ## New in main
 
 * Add support for tasks depending on directories
+* New `fast_dirs` mode in TaskManager for cheaper directory checks 
 * Add progress callback
 * Add support for passing blocks to Tasks:
 
diff --git a/TODO.md b/TODO.md
index c4434f3..91ab8a9 100644
--- a/TODO.md
+++ b/TODO.md
@@ -6,9 +6,9 @@
   [Fiber Metrics](https://github.com/didactic-drunk/fiber_metrics.cr)
 * Add wildcard dependencies (depend on all files / tasks matching a pattern)
 * Mark tasks as stale if the OUTPUT is modified since last run
-* Allow a "shallow" mode for directory dependencies, which hashes just a list of contents
-  and not the contents of the files themselves.
 
+* ~~Allow a "shallow" mode for directory dependencies, which hashes just a list of contents~~
+  ~~and not the contents of the files themselves.~~
 * ~~Add directory dependencies (depend on all files in the tree)~~
 * ~~Fix parallel `run_all` flag~~
 * ~~Add a faster stale input check using file dates instead of hashes (like make)~~
diff --git a/spec/croupier_spec.cr b/spec/croupier_spec.cr
index 66bfd04..65df3d3 100644
--- a/spec/croupier_spec.cr
+++ b/spec/croupier_spec.cr
@@ -785,6 +785,33 @@ describe "TaskManager" do
           id: "t1"
         )
         TaskManager.scan_inputs.should eq({"dir" => "da39a3ee5e6b4b0d3255bfef95601890afd80709"})
+        File.write("dir/input", "foo")
+        TaskManager.scan_inputs.should eq({"dir" => "7e0dbd57e84798fe1a40bb453dcf51f2569a3a2e"})
+        # This mode doesn't ignore file contents
+        File.write("dir/input", "bar")
+        TaskManager.scan_inputs.should eq({"dir" => "63734eec74b627be2865c006e11b270747b4df2c"})
+        Dir.mkdir("dir/dir1")
+        TaskManager.scan_inputs.should eq({"dir" => "05cfe846d65930c8a0be1da2b8aa16ee21d0cbdd"})
+      end
+    end
+    it "should hash directories in fast_dirs mode" do
+      with_scenario("empty") do
+        TaskManager.fast_dirs = true
+        Dir.mkdir("dir")
+        Task.new(
+          inputs: ["dir"],
+          always_run: true,
+          proc: nil,
+          id: "t1"
+        )
+        TaskManager.scan_inputs.should eq({"dir" => "da39a3ee5e6b4b0d3255bfef95601890afd80709"})
+        File.write("dir/input", "foo")
+        TaskManager.scan_inputs.should eq({"dir" => "18e96066fa04ae6c67b5cdcfb02c7c5646ae2402"})
+        # This mode ignores file contents
+        File.write("dir/input", "bar")
+        TaskManager.scan_inputs.should eq({"dir" => "18e96066fa04ae6c67b5cdcfb02c7c5646ae2402"})
+        Dir.mkdir("dir/dir1")
+        TaskManager.scan_inputs.should eq({"dir" => "f6fa5320de20f424aaab984f56d470386ca9cb96"})
       end
     end
   end
diff --git a/src/croupier.cr b/src/croupier.cr
index adfc644..92c71c7 100644
--- a/src/croupier.cr
+++ b/src/croupier.cr
@@ -108,7 +108,7 @@ module Croupier
       # Refuse to merge if this task or any of the colliding ones
       # are not mergeable
       raise "Can't merge task #{self} with #{to_merge[..-2].map(&.to_s)}" \
-        if to_merge.size > 1 && to_merge.any? { |t| !t.mergeable? }
+         if to_merge.size > 1 && to_merge.any? { |t| !t.mergeable? }
       reduced = to_merge.reduce { |t1, t2| t1.merge t2 }
       reduced.keys.each { |k| TaskManager.tasks[k] = reduced }
     end
@@ -302,6 +302,8 @@ module Croupier
     property? fast_mode : Bool = false
     # If true, it's running in auto mode
     property? auto_mode : Bool = false
+    # If true, directories depend on a list of files, not its contents
+    property? fast_dirs : Bool = false
     # If set, it's called after every task finishes
     property progress_callback : Proc(String, Nil) = ->(_id : String) {}
 
@@ -502,9 +504,13 @@ module Croupier
         else
           if File.directory? path
             digest = Digest::SHA1.digest do |ctx|
-              # Hash *everything* in the directory (this will be slow)
-              Dir.glob("#{path}/**/*").each do |f|
-                ctx.update File.read(path) if File.file? f
+              # Hash the directory tree
+              ctx.update(Dir.glob("#{path}/**/*").join("\n"))
+              if !@fast_dirs
+                # Hash *everything* in the directory (this will be slow)
+                Dir.glob("#{path}/**/*").each do |f|
+                  ctx.update File.read(f) if File.file? f
+                end
               end
             end
             hash[path] = digest.hexstring
@@ -530,7 +536,7 @@ module Croupier
           !File.exists?(input)
       }
       raise "Can't run: Unknown inputs #{bad_inputs.join(", ")}" \
-        unless bad_inputs.empty?
+         unless bad_inputs.empty?
     end
 
     # Run all stale tasks in dependency order