diff --git a/src/file_utils.cpp b/src/file_utils.cpp
index 15b30e3b6..8a078fe18 100644
--- a/src/file_utils.cpp
+++ b/src/file_utils.cpp
@@ -28,11 +28,24 @@ bool file_exists(const std::string& filename)
 
 std::string get_file_extension(const std::string& filename)
 {
+  // try our best to work on windows...
+#if defined(_WIN32) || defined(_WIN64)
+  const char sep_char = '\\';
+#else
+  const char sep_char = '/';
+#endif
+
   // check that at least one letter is present
   const auto last_period_pos = filename.find_last_of('.');
+  const auto last_sep_pos = filename.find_last_of(sep_char);
 
-  // no file extension
-  if (last_period_pos == std::string::npos)
+  // no file extension. In the first case, we are only given
+  // a file name. In the second, we have been given a file path.
+  // If that's the case, periods are allowed in directory names,
+  // but have the interpretation as preceding a file extension
+  // after the last separator.
+  if (last_period_pos == std::string::npos ||
+      (last_sep_pos < std::string::npos && last_period_pos < last_sep_pos))
     return "";
 
   const std::string ending = filename.substr(last_period_pos + 1);
diff --git a/tests/cpp_unit_tests/test_file_utils.cpp b/tests/cpp_unit_tests/test_file_utils.cpp
index 69d9b5a59..3b7a74346 100644
--- a/tests/cpp_unit_tests/test_file_utils.cpp
+++ b/tests/cpp_unit_tests/test_file_utils.cpp
@@ -12,6 +12,8 @@ TEST_CASE("Test get_file_extension")
   REQUIRE(get_file_extension("wasssssup_lol") == "");
   REQUIRE(get_file_extension("has_directory/secret_file") == "");
   REQUIRE(get_file_extension("lovely.dir/extensionless_file") == "");
+  REQUIRE(get_file_extension("lovely.dir/statepoint.20.h5") == "h5");
+  REQUIRE(get_file_extension("lovely.dir/asdf123.cpp") == "cpp");
 }
 
 TEST_CASE("Test dir_exists")
@@ -25,5 +27,6 @@ TEST_CASE("Test dir_exists")
 
 TEST_CASE("Test file_exists")
 {
-  // TODO make a file test it exists, delete it
+  // Note: not clear how to portably test where a file should exist.
+  REQUIRE(!file_exists("./should_not_exist/really_do_not_make_this_please"));
 }