diff --git a/test/format-test.cc b/test/format-test.cc
index 24239336..9992cecd 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -129,6 +129,8 @@ class TestString {
   }
 };
 
+extern char array_of_unknown_size[];
+
 TEST(ArrayTest, Ctor) {
   Array<char, 123> array;
   EXPECT_EQ(0u, array.size());
@@ -419,6 +421,12 @@ TEST(WriterTest, WriteWideString) {
   //fmt::WWriter() << "abc";
 }
 
+TEST(WriterTest, WriteArrayOfUnknownSize) {
+  fmt::Writer w;
+  w.write("{}", array_of_unknown_size);
+  EXPECT_EQ(array_of_unknown_size, w.str());
+}
+
 TEST(WriterTest, bin) {
   using fmt::bin;
   EXPECT_EQ("1100101011111110", (Writer() << bin(0xcafe)).str());
@@ -1523,3 +1531,6 @@ TEST(FormatTest, FormatMessageExample) {
   EXPECT_EQ("[42] something happened",
       FormatMessage(42, "{} happened", "something"));
 }
+
+// This should be at the end of the file to make the array size unknown above.
+char array_of_unknown_size[] = "abc";