diff --git a/test/test_filebuf.cpp b/test/test_filebuf.cpp
index 1aabe42..763ae20 100644
--- a/test/test_filebuf.cpp
+++ b/test/test_filebuf.cpp
@@ -143,14 +143,14 @@ void test_64_bit_seek(const std::string& filepath)
     // Create a value which does not fit into a 32 bit value.
     // Use an unsigned intermediate to have the truncation defined to wrap to 0
     using unsigned_off_type = std::make_unsigned<nw::filebuf::off_type>::type;
-    const nw::filebuf::off_type offset = static_cast<unsigned_off_type>(std::uint64_t(1) << 33u);
+    nw::filebuf::off_type offset = static_cast<unsigned_off_type>(std::uint64_t(1) << 33u);
 
 #ifdef BOOST_MSVC
 #pragma warning(push)
 #pragma warning(disable : 4127)
 #endif
     // coverity[result_independent_of_operands]
-    if((offset == nw::filebuf::off_type(0)))
+    if(offset == nw::filebuf::off_type(0))
         return; // Can't use 64 bit offsets throught the API, so don't test anything
 #ifdef BOOST_MSVC
 #pragma warning(pop)
@@ -169,6 +169,11 @@ void test_64_bit_seek(const std::string& filepath)
         TEST(buf.pubseekoff(0, std::ios_base::cur) == knownPos);
     else
     {
+#if !BOOST_NOWIDE_USE_FILEBUF_REPLACEMENT
+        // libc++ may truncate the 64 bit value when calling fseek which yields an offset of 0
+        if(newPos == knownPos)
+            offset = 0; // LCOV_EXCL_LINE
+#endif
         TEST(newPos == offset + knownPos);
         TEST(buf.pubseekoff(0, std::ios_base::cur) == newPos);
     }
@@ -228,6 +233,7 @@ void test_swap(const std::string& filepath)
         TEST(buf1.sputc('B') == 'B');
         TEST(buf2.sbumpc() == 'H');
         buf1.swap(buf2);
+        // Trying to read in write mode or other way round should fail
         TEST(buf1.sputc('x') == eof);
         TEST(buf2.sbumpc() == eof);
         TEST(buf1.sbumpc() == 'e');
@@ -311,5 +317,9 @@ void test_main(int, char** argv, char**)
     test_pubseekpos(exampleFilename);
     test_pubseekoff(exampleFilename);
     test_64_bit_seek(exampleFilename);
+// These tests are only useful for the nowide filebuf and are known to fail for
+// std::filebuf due to bugs in libc++
+#if BOOST_NOWIDE_USE_FILEBUF_REPLACEMENT
     test_swap(exampleFilename);
+#endif
 }