diff --git a/builtin-grep.c b/builtin-grep.c
index 761799d..1df25b0 100644
--- a/builtin-grep.c
+++ b/builtin-grep.c
@@ -631,7 +631,7 @@
 	struct grep_opt *grep_opt = opt->value;
 	FILE *patterns;
 	int lno = 0;
-	struct strbuf sb;
+	struct strbuf sb = STRBUF_INIT;
 
 	patterns = fopen(arg, "r");
 	if (!patterns)
diff --git a/t/t7002-grep.sh b/t/t7002-grep.sh
index ae56a36..ae5290a 100755
--- a/t/t7002-grep.sh
+++ b/t/t7002-grep.sh
@@ -213,6 +213,72 @@
 	test_cmp expected actual
 '
 
+test_expect_success 'grep -f, non-existent file' '
+	test_must_fail git grep -f patterns
+'
+
+cat >expected <<EOF
+file:foo mmap bar
+file:foo_mmap bar
+file:foo_mmap bar mmap
+file:foo mmap bar_mmap
+file:foo_mmap bar mmap baz
+EOF
+
+cat >pattern <<EOF
+mmap
+EOF
+
+test_expect_success 'grep -f, one pattern' '
+	git grep -f pattern >actual &&
+	test_cmp expected actual
+'
+
+cat >expected <<EOF
+file:foo mmap bar
+file:foo_mmap bar
+file:foo_mmap bar mmap
+file:foo mmap bar_mmap
+file:foo_mmap bar mmap baz
+t/a/v:vvv
+t/v:vvv
+v:vvv
+EOF
+
+cat >patterns <<EOF
+mmap
+vvv
+EOF
+
+test_expect_success 'grep -f, multiple patterns' '
+	git grep -f patterns >actual &&
+	test_cmp expected actual
+'
+
+cat >expected <<EOF
+file:foo mmap bar
+file:foo_mmap bar
+file:foo_mmap bar mmap
+file:foo mmap bar_mmap
+file:foo_mmap bar mmap baz
+t/a/v:vvv
+t/v:vvv
+v:vvv
+EOF
+
+cat >patterns <<EOF
+
+mmap
+
+vvv
+
+EOF
+
+test_expect_success 'grep -f, ignore empty lines' '
+	git grep -f patterns >actual &&
+	test_cmp expected actual
+'
+
 cat >expected <<EOF
 y:y yy
 --