diff --git a/public/build.c b/public/build.c
index 237fd0ee..756fc71c 100644
--- a/public/build.c
+++ b/public/build.c
@@ -13,6 +13,7 @@ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.
 */
 
+#include <stdio.h>
 #include "crtlib.h"
 #include "buildenums.h"
 
@@ -38,9 +39,31 @@ int Q_buildnum_date( const char *date )
 	b = d + (int)((y - 1) * 365.25f );
 
 	if((( y % 4 ) == 0 ) && m > 1 )
-	{
 		b += 1;
-	}
+	b -= 41728; // Apr 1 2015
+
+	return b;
+}
+
+int Q_buildnum_iso( const char *date )
+{
+	int y, m, d, b, i;
+
+	if( sscanf( date, "%d-%d-%d", &y, &m, &d ) != 3 || y <= 1900 || m <= 0 || d <= 0 )
+		return -1;
+
+	// fixup day and month
+	m--;
+	d--;
+
+	for( i = 0; i < m; i++ )
+		d += mond[i];
+
+	y -= 1900;
+	b = d + (int)((y - 1) * 365.25f );
+
+	if((( y % 4 ) == 0 ) && m > 1 )
+		b += 1;
 	b -= 41728; // Apr 1 2015
 
 	return b;
diff --git a/public/crtlib.h b/public/crtlib.h
index 3216d97e..b19152bd 100644
--- a/public/crtlib.h
+++ b/public/crtlib.h
@@ -57,6 +57,7 @@ enum
 //
 int Q_buildnum( void );
 int Q_buildnum_date( const char *date );
+int Q_buildnum_iso( const char *date );
 int Q_buildnum_compat( void );
 const char *Q_PlatformStringByID( const int platform );
 const char *Q_buildos( void );
diff --git a/public/tests/test_build.c b/public/tests/test_build.c
index 016505dc..ee3b0f40 100644
--- a/public/tests/test_build.c
+++ b/public/tests/test_build.c
@@ -180,8 +180,14 @@ int main( void )
 	if( Q_buildnum_date( "Apr 02 2015" ) != 1 )
 		return 201;
 
-	if( Q_buildnum_date( "Apr 17 2023" ) != 2938 )
+	if( Q_buildnum_date( "Apr 02 2015" ) != Q_buildnum_iso( "2015-04-02 21:19:10 +0300" ))
 		return 202;
 
+	if( Q_buildnum_date( "Apr 17 2023" ) != 2938 )
+		return 203;
+
+	if( Q_buildnum_date( "Apr 17 2023" ) != Q_buildnum_iso( "2023-04-17 21:19:10 +0300" ))
+		return 204;
+
 	return EXIT_SUCCESS;
 }