diff --git a/BUILDING.md b/BUILDING.md
index 8e43eb73d04434..ae94b8846e97d2 100644
--- a/BUILDING.md
+++ b/BUILDING.md
@@ -403,7 +403,7 @@ by providing the name of a subsystem:
 
 ```text
 $ make coverage-clean
-$ NODE_V8_COVERAGE=coverage/tmp tools/test.py -J --mode=release child-process
+$ NODE_V8_COVERAGE=coverage/tmp tools/test.py --mode=release child-process
 $ make coverage-report-js
 ```
 
diff --git a/Makefile b/Makefile
index 688bfc6bcbe3bd..be131195018fa1 100644
--- a/Makefile
+++ b/Makefile
@@ -23,7 +23,7 @@ FIND ?= find
 ifdef JOBS
 	PARALLEL_ARGS = -j $(JOBS)
 else
-	PARALLEL_ARGS = -J
+	PARALLEL_ARGS =
 endif
 
 ifdef ENABLE_V8_TAP
diff --git a/tools/test.py b/tools/test.py
index 8ca1f58e9a1223..f204004c7a63f1 100755
--- a/tools/test.py
+++ b/tools/test.py
@@ -1362,9 +1362,9 @@ def BuildOptions():
       default="")
   result.add_option("--warn-unused", help="Report unused rules",
       default=False, action="store_true")
-  result.add_option("-j", help="The number of parallel tasks to run",
-      default=1, type="int")
-  result.add_option("-J", help="Run tasks in parallel on all cores",
+  result.add_option("-j", help="The number of parallel tasks to run, 0=use number of cores",
+      default=0, type="int")
+  result.add_option("-J", help="For legacy compatibility, has no effect",
       default=False, action="store_true")
   result.add_option("--time", help="Print timing information after running",
       default=False, action="store_true")
@@ -1423,11 +1423,16 @@ def ProcessOptions(options):
     if options.run[0] >= options.run[1]:
       print("The test group to run (n) must be smaller than number of groups (m).")
       return False
-  if options.J:
+  if options.j == 0:
     # inherit JOBS from environment if provided. some virtualised systems
     # tends to exaggerate the number of available cpus/cores.
     cores = os.environ.get('JOBS')
     options.j = int(cores) if cores is not None else multiprocessing.cpu_count()
+  elif options.J:
+    # If someone uses -j and legacy -J, let them know that we will be respecting
+    # -j and ignoring -J, which is the opposite of what we used to do before -J
+    # became a legacy no-op.
+    print('Warning: Legacy -J option is ignored. Using the -j option.')
   if options.flaky_tests not in [RUN, SKIP, DONTCARE]:
     print("Unknown flaky-tests mode %s" % options.flaky_tests)
     return False
diff --git a/vcbuild.bat b/vcbuild.bat
index 604843027cb1e5..49a05602d6ddc1 100644
--- a/vcbuild.bat
+++ b/vcbuild.bat
@@ -92,9 +92,9 @@ if /i "%1"=="nosnapshot"    set nosnapshot=1&goto arg-ok
 if /i "%1"=="noetw"         set noetw=1&goto arg-ok
 if /i "%1"=="ltcg"          set ltcg=1&goto arg-ok
 if /i "%1"=="licensertf"    set licensertf=1&goto arg-ok
-if /i "%1"=="test"          set test_args=%test_args% -J %common_test_suites%&set lint_cpp=1&set lint_js=1&set lint_md=1&goto arg-ok
-if /i "%1"=="test-ci-native" set test_args=%test_args% %test_ci_args% -J -p tap --logfile test.tap %CI_NATIVE_SUITES% %CI_DOC%&set build_addons=1&set build_js_native_api_tests=1&set build_node_api_tests=1&set cctest_args=%cctest_args% --gtest_output=xml:cctest.junit.xml&goto arg-ok
-if /i "%1"=="test-ci-js"    set test_args=%test_args% %test_ci_args% -J -p tap --logfile test.tap %CI_JS_SUITES%&set no_cctest=1&goto arg-ok
+if /i "%1"=="test"          set test_args=%test_args% %common_test_suites%&set lint_cpp=1&set lint_js=1&set lint_md=1&goto arg-ok
+if /i "%1"=="test-ci-native" set test_args=%test_args% %test_ci_args% -p tap --logfile test.tap %CI_NATIVE_SUITES% %CI_DOC%&set build_addons=1&set build_js_native_api_tests=1&set build_node_api_tests=1&set cctest_args=%cctest_args% --gtest_output=xml:cctest.junit.xml&goto arg-ok
+if /i "%1"=="test-ci-js"    set test_args=%test_args% %test_ci_args% -p tap --logfile test.tap %CI_JS_SUITES%&set no_cctest=1&goto arg-ok
 if /i "%1"=="build-addons"   set build_addons=1&goto arg-ok
 if /i "%1"=="build-js-native-api-tests"   set build_js_native_api_tests=1&goto arg-ok
 if /i "%1"=="build-node-api-tests"   set build_node_api_tests=1&goto arg-ok
@@ -103,7 +103,7 @@ if /i "%1"=="test-doc"      set test_args=%test_args% %CI_DOC%&set doc=1&&set li
 if /i "%1"=="test-js-native-api"   set test_args=%test_args% js-native-api&set build_js_native_api_tests=1&goto arg-ok
 if /i "%1"=="test-node-api"   set test_args=%test_args% node-api&set build_node_api_tests=1&goto arg-ok
 if /i "%1"=="test-benchmark" set test_args=%test_args% benchmark&goto arg-ok
-if /i "%1"=="test-simple"   set test_args=%test_args% sequential parallel -J&goto arg-ok
+if /i "%1"=="test-simple"   set test_args=%test_args% sequential parallel&goto arg-ok
 if /i "%1"=="test-message"  set test_args=%test_args% message&goto arg-ok
 if /i "%1"=="test-tick-processor" set test_args=%test_args% tick-processor&goto arg-ok
 if /i "%1"=="test-internet" set test_args=%test_args% internet&goto arg-ok
@@ -644,7 +644,7 @@ if defined test_node_inspect goto node-test-inspect
 goto node-tests
 
 :node-check-deopts
-python tools\test.py --mode=release --check-deopts parallel sequential -J
+python tools\test.py --mode=release --check-deopts parallel sequential
 if defined test_node_inspect goto node-test-inspect
 goto node-tests