diff --git a/include/spdlog/sinks/hourly_file_sink.h b/include/spdlog/sinks/hourly_file_sink.h
index 43c6a638..3de176b0 100644
--- a/include/spdlog/sinks/hourly_file_sink.h
+++ b/include/spdlog/sinks/hourly_file_sink.h
@@ -22,16 +22,15 @@ namespace spdlog {
 namespace sinks {
 
 /*
- * Generator of Hourly log file names in format basename.YYYY-MM-DD-HH.ext
+ * Generator of Hourly log file names in format basename_YYYY-MM-DD_HH.ext
  */
 struct hourly_filename_calculator {
-    // Create filename for the form basename.YYYY-MM-DD-H
     static filename_t calc_filename(const filename_t &filename, const tm &now_tm) {
         filename_t basename, ext;
         std::tie(basename, ext) = details::file_helper::split_by_extension(filename);
         std::basic_ostringstream<filename_t::value_type> oss;        
-        oss << basename.native() << '-' << std::setfill(SPDLOG_FILENAME_T('0')) << std::setw(4) << now_tm.tm_year + 1900 << '-'
-            << std::setw(2) << now_tm.tm_mon + 1 << '-' << std::setw(2) << now_tm.tm_mday << '-' << std::setw(2) << now_tm.tm_hour
+        oss << basename.native() << '_' << std::setfill(SPDLOG_FILENAME_T('0')) << std::setw(4) << now_tm.tm_year + 1900 << '-'
+            << std::setw(2) << now_tm.tm_mon + 1 << '-' << std::setw(2) << now_tm.tm_mday << '_' << std::setw(2) << now_tm.tm_hour
             << ext.native();
         return oss.str();        
     }
diff --git a/tests/test_daily_and_rotation_loggers.cpp b/tests/test_daily_and_rotation_loggers.cpp
index 64154127..757404b5 100644
--- a/tests/test_daily_and_rotation_loggers.cpp
+++ b/tests/test_daily_and_rotation_loggers.cpp
@@ -5,6 +5,7 @@
 #include "includes.h"
 #include "spdlog/sinks/daily_file_sink.h"
 #include "spdlog/sinks/rotating_file_sink.h"
+#include "spdlog/sinks/hourly_file_sink.h"
 
 using filename_memory_buf_t = spdlog::memory_buf_t;
 
@@ -95,6 +96,19 @@ TEST_CASE("daily_file_sink::daily_filename_calculator", "[daily_file_sink]") {
      std::match_results<spdlog::filename_t::string_type::const_iterator> match;
      REQUIRE(std::regex_match(filename.native(), match, re));     
 }
+
+
+TEST_CASE("hourly_file_sink::hourly_filename_calculator", "[hrouly_file_sink]") {
+    // daily_YYYY-MM-DD_hh-mm.txt
+    auto filename =
+        spdlog::sinks::hourly_filename_calculator::calc_filename(SPDLOG_FILENAME_T("hourly.txt"), spdlog::details::os::localtime());
+    // date regex based on https://www.regular-expressions.info/dates.html
+    std::basic_regex<spdlog::filename_t::value_type> re(
+        SPDLOG_FILENAME_T(R"(^hourly_(19|20)\d\d-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01])_\d\d\.txt$)"));
+
+    std::match_results<spdlog::filename_t::string_type::const_iterator> match;
+    REQUIRE(std::regex_match(filename.native(), match, re));
+}
 #endif
 
 TEST_CASE("daily_file_sink::daily_filename_format_calculator", "[daily_file_sink]") {