diff --git a/.gn b/.gn
index 07070a11f8..bebb5388f9 100644
--- a/.gn
+++ b/.gn
@@ -32,10 +32,6 @@ default_args = {
   treat_warnings_as_errors = false
   rust_treat_warnings_as_errors = true
 
-  # Enable Jumbo build by default
-  # https://chromium.googlesource.com/chromium/src/+/master/docs/jumbo.md
-  use_jumbo_build = true
-
   # https://cs.chromium.org/chromium/src/docs/ccache_mac.md
   clang_use_chrome_plugins = false
 
diff --git a/tools/setup.py b/tools/setup.py
index dbb44c5e19..3b0246f515 100755
--- a/tools/setup.py
+++ b/tools/setup.py
@@ -104,7 +104,9 @@ def generate_gn_args(mode):
     if mode == "release":
         out += ["is_official_build=true"]
     elif mode == "debug":
-        pass
+        # Enable Jumbo build by default in debug mode for faster build.
+        # https://chromium.googlesource.com/chromium/src/+/master/docs/jumbo.md
+        out += ["use_jumbo_build=true"]
     else:
         print "Bad mode {}. Use 'release' or 'debug' (default)" % mode
         sys.exit(1)