diff --git a/Documentation/git-grep.txt b/Documentation/git-grep.txt
index de628741fa..eb5412724f 100644
--- a/Documentation/git-grep.txt
+++ b/Documentation/git-grep.txt
@@ -59,8 +59,8 @@ grep.extendedRegexp::
 	other than 'default'.
 
 grep.threads::
-	Number of grep worker threads to use.  If unset (or set to 0),
-	8 threads are used by default (for now).
+	Number of grep worker threads to use. If unset (or set to 0), Git will
+	use as many threads as the number of logical cores available.
 
 grep.fullName::
 	If set to true, enable `--full-name` option by default.
diff --git a/builtin/grep.c b/builtin/grep.c
index a85b710b48..629eaf5dbc 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -33,7 +33,6 @@ static char const * const grep_usage[] = {
 
 static int recurse_submodules;
 
-#define GREP_NUM_THREADS_DEFAULT 8
 static int num_threads;
 
 static pthread_t *threads;
@@ -1064,7 +1063,7 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 	} else if (num_threads < 0)
 		die(_("invalid number of threads specified (%d)"), num_threads);
 	else if (num_threads == 0)
-		num_threads = HAVE_THREADS ? GREP_NUM_THREADS_DEFAULT : 1;
+		num_threads = HAVE_THREADS ? online_cpus() : 1;
 
 	if (num_threads > 1) {
 		if (!HAVE_THREADS)