diff --git a/tests/regex_test.cpp b/tests/regex_test.cpp
index 4a4409e..0e7f8dd 100644
--- a/tests/regex_test.cpp
+++ b/tests/regex_test.cpp
@@ -46,3 +46,14 @@
   ASSERT_EQ(2, matches[0].rm_eo);
   regfree(&re);
 }
+
+TEST(regex, regerror_NULL_0) {
+  regex_t re;
+  int error = regcomp(&re, "*", REG_EXTENDED);
+  ASSERT_NE(0, error);
+
+  // Passing a null pointer and a size of 0 is a legitimate way to ask
+  // how large a buffer we would need for the error message.
+  int error_length = regerror(error, &re, nullptr, 0);
+  ASSERT_GT(error_length, 0);
+}