diff --git a/python/servo/build_commands.py b/python/servo/build_commands.py
index 7dd4b3995f5..009c4b76c40 100644
--- a/python/servo/build_commands.py
+++ b/python/servo/build_commands.py
@@ -56,7 +56,7 @@ class MachCommands(CommandBase):
             opts += ["-v"]
 
         features = []
-        if debug_mozjs:
+        if debug_mozjs or self.config["build"]["debug-mozjs"]:
             features += ["script/debugmozjs"]
 
         if features:
diff --git a/python/servo/command_base.py b/python/servo/command_base.py
index d78c0e13a1c..96cf287b329 100644
--- a/python/servo/command_base.py
+++ b/python/servo/command_base.py
@@ -79,6 +79,8 @@ class CommandBase(object):
         self.config.setdefault("build", {})
         self.config["build"].setdefault("android", False)
 
+        self.config["build"].setdefault("debug-mozjs", False)
+
         self.config.setdefault("android", {})
         self.config["android"].setdefault("sdk", "")
         self.config["android"].setdefault("ndk", "")
diff --git a/servobuild.example b/servobuild.example
index 2d0ceeba46f..db3aba17f4f 100644
--- a/servobuild.example
+++ b/servobuild.example
@@ -12,6 +12,8 @@ cargo-root = "/path/to/cargo"
 [build]
 # Set "android = true" or use `mach build --android` to build the Android app.
 android = false
+# Set "debug-mozjs" or use `mach build --debug-mozjs` to build a debug spidermonkey.
+debug-mozjs = false
 
 # Android information
 [android]