diff --git a/src/jrd/SysFunction.cpp b/src/jrd/SysFunction.cpp
index 7831477537e..bafc1f05cfa 100644
--- a/src/jrd/SysFunction.cpp
+++ b/src/jrd/SysFunction.cpp
@@ -3985,7 +3985,7 @@ dsc* evlDateDiff(thread_db* tdbb, const SysFunction* function, const NestValueAr
 
 		case blr_extract_millisecond:
 			result = (SINT64) ONE_DAY *
-				(timestamp2.value().timestamp_date - timestamp1.value().timestamp_date) * 1000;
+				(timestamp2.value().timestamp_date - timestamp1.value().timestamp_date) * ISC_TIME_SECONDS_PRECISION;
 			result += (SINT64) timestamp2.value().timestamp_time - (SINT64) timestamp1.value().timestamp_time;
 			scale = ISC_TIME_SECONDS_PRECISION_SCALE + 3;
 			break;