diff --git a/builtin-grep.c b/builtin-grep.c
index 01be9bf7ff..9a9e3fccd5 100644
--- a/builtin-grep.c
+++ b/builtin-grep.c
@@ -433,7 +433,11 @@ static int external_grep(struct grep_opt *opt, const char **paths, int cached)
 
 		if (opt->color_external && strlen(opt->color_external) > 0)
 			push_arg(opt->color_external);
+	} else {
+		unsetenv("GREP_COLOR");
+		unsetenv("GREP_COLORS");
 	}
+	unsetenv("GREP_OPTIONS");
 
 	hit = 0;
 	argc = nr;
diff --git a/t/t7002-grep.sh b/t/t7002-grep.sh
index ae5290ab43..dd0da6c0bf 100755
--- a/t/t7002-grep.sh
+++ b/t/t7002-grep.sh
@@ -213,6 +213,11 @@ test_expect_success 'grep -e A --and --not -e B' '
 	test_cmp expected actual
 '
 
+test_expect_success 'grep should ignore GREP_OPTIONS' '
+	GREP_OPTIONS=-v git grep " mmap bar\$" >actual &&
+	test_cmp expected actual
+'
+
 test_expect_success 'grep -f, non-existent file' '
 	test_must_fail git grep -f patterns
 '