diff --git a/tests/wchar_test.cpp b/tests/wchar_test.cpp
index 20566f2..0a63b00 100644
--- a/tests/wchar_test.cpp
+++ b/tests/wchar_test.cpp
@@ -16,6 +16,7 @@
 
 #include <gtest/gtest.h>
 
+#include <errno.h>
 #include <limits.h>
 #include <wchar.h>
 
@@ -55,3 +56,102 @@
   EXPECT_EQ(1U, wcrtomb(bytes, L'h', NULL));
   EXPECT_EQ('h', bytes[0]);
 }
+
+TEST(wchar, wcstombs_wcrtombs) {
+  wchar_t chars[] = { L'h', L'e', L'l', L'l', L'o', 0 };
+  wchar_t bad_chars[] = { L'h', L'i', 666, 0 };
+  const wchar_t* src;
+  char bytes[BUFSIZ];
+
+  // Given a NULL destination, these functions count valid characters.
+  EXPECT_EQ(5U, wcstombs(NULL, chars, 0));
+  EXPECT_EQ(5U, wcstombs(NULL, chars, 4));
+  EXPECT_EQ(5U, wcstombs(NULL, chars, 256));
+  src = chars;
+  EXPECT_EQ(5U, wcsrtombs(NULL, &src, 0, NULL));
+  EXPECT_EQ(&chars[0], src);
+  src = chars;
+  EXPECT_EQ(5U, wcsrtombs(NULL, &src, 4, NULL));
+  EXPECT_EQ(&chars[0], src);
+  src = chars;
+  EXPECT_EQ(5U, wcsrtombs(NULL, &src, 256, NULL));
+  EXPECT_EQ(&chars[0], src);
+
+  // An unrepresentable char just returns an error from wcstombs...
+  errno = 0;
+  EXPECT_EQ(static_cast<size_t>(-1), wcstombs(NULL, bad_chars, 0));
+  EXPECT_EQ(EILSEQ, errno);
+  errno = 0;
+  EXPECT_EQ(static_cast<size_t>(-1), wcstombs(NULL, bad_chars, 256));
+  EXPECT_EQ(EILSEQ, errno);
+
+  // And wcsrtombs doesn't tell us where it got stuck because we didn't ask it
+  // to actually convert anything...
+  errno = 0;
+  src = bad_chars;
+  EXPECT_EQ(static_cast<size_t>(-1), wcsrtombs(NULL, &src, 0, NULL));
+  EXPECT_EQ(&bad_chars[0], src);
+  EXPECT_EQ(EILSEQ, errno);
+  errno = 0;
+  src = bad_chars;
+  EXPECT_EQ(static_cast<size_t>(-1), wcsrtombs(NULL, &src, 256, NULL));
+  EXPECT_EQ(&bad_chars[0], src);
+  EXPECT_EQ(EILSEQ, errno);
+
+  // Okay, now let's test actually converting something...
+  memset(bytes, 'x', sizeof(bytes));
+  EXPECT_EQ(0U, wcstombs(bytes, chars, 0));
+  memset(bytes, 'x', sizeof(bytes));
+  EXPECT_EQ(4U, wcstombs(bytes, chars, 4));
+  bytes[5] = 0;
+  EXPECT_STREQ("hellx", bytes);
+  memset(bytes, 'x', sizeof(bytes));
+  EXPECT_EQ(5U, wcstombs(bytes, chars, 256));
+  EXPECT_STREQ("hello", bytes);
+  memset(bytes, 'x', sizeof(bytes));
+  EXPECT_EQ(5U, wcstombs(bytes, chars, 6));
+  EXPECT_STREQ("hello", bytes);
+  errno = 0;
+  memset(bytes, 'x', sizeof(bytes));
+  EXPECT_EQ(static_cast<size_t>(-1), wcstombs(bytes, bad_chars, 256));
+  EXPECT_EQ(EILSEQ, errno);
+  bytes[3] = 0;
+  EXPECT_STREQ("hix", bytes);
+
+  // wcsrtombs is a bit more informative...
+  memset(bytes, 'x', sizeof(bytes));
+  src = chars;
+  EXPECT_EQ(0U, wcsrtombs(bytes, &src, 0, NULL));
+  EXPECT_EQ(&chars[0], src); // No input consumed.
+  EXPECT_EQ(EILSEQ, errno);
+
+  memset(bytes, 'x', sizeof(bytes));
+  src = chars;
+  EXPECT_EQ(4U, wcsrtombs(bytes, &src, 4, NULL));
+  EXPECT_EQ(&chars[4], src); // Some input consumed.
+  EXPECT_EQ(EILSEQ, errno);
+  bytes[5] = 0;
+  EXPECT_STREQ("hellx", bytes);
+
+  memset(bytes, 'x', sizeof(bytes));
+  src = chars;
+  EXPECT_EQ(5U, wcsrtombs(bytes, &src, 256, NULL));
+  EXPECT_EQ(NULL, src); // All input consumed!
+  EXPECT_EQ(EILSEQ, errno);
+  EXPECT_STREQ("hello", bytes);
+
+  memset(bytes, 'x', sizeof(bytes));
+  src = chars;
+  EXPECT_EQ(5U, wcsrtombs(bytes, &src, 6, NULL));
+  EXPECT_EQ(NULL, src); // All input consumed.
+  EXPECT_EQ(EILSEQ, errno);
+  EXPECT_STREQ("hello", bytes);
+
+  memset(bytes, 'x', sizeof(bytes));
+  src = bad_chars;
+  EXPECT_EQ(static_cast<size_t>(-1), wcsrtombs(bytes, &src, 256, NULL));
+  EXPECT_EQ(&bad_chars[2], src);
+  EXPECT_EQ(EILSEQ, errno);
+  bytes[3] = 0;
+  EXPECT_STREQ("hix", bytes);
+}