--- src/backend/utils/adt/timestamp.c
+++ src/backend/utils/adt/timestamp.c
@@ -2412,7 +2412,7 @@
 			case DTK_YEAR:
 				tm->tm_mon = 1;
 			case DTK_QUARTER:
-				tm->tm_mon = (3 * (tm->tm_mon / 4)) + 1;
+				tm->tm_mon = (3 * ((tm->tm_mon - 1) / 3)) + 1;
 			case DTK_MONTH:
 				tm->tm_mday = 1;
 			case DTK_DAY:
@@ -2505,7 +2505,7 @@
 			case DTK_YEAR:
 				tm->tm_mon = 1;
 			case DTK_QUARTER:
-				tm->tm_mon = (3 * (tm->tm_mon / 4)) + 1;
+				tm->tm_mon = (3 * ((tm->tm_mon - 1) / 3)) + 1;
 			case DTK_MONTH:
 				tm->tm_mday = 1;
 			case DTK_DAY:
@@ -2598,7 +2598,7 @@
 				case DTK_YEAR:
 					tm->tm_mon = 0;
 				case DTK_QUARTER:
-					tm->tm_mon = (3 * (tm->tm_mon / 4));
+					tm->tm_mon = (3 * (tm->tm_mon / 3));
 				case DTK_MONTH:
 					tm->tm_mday = 0;
 				case DTK_DAY:
@@ -3175,7 +3175,7 @@
 					break;
 
 				case DTK_QUARTER:
-					result = (tm->tm_mon / 4) + 1;
+					result = (tm->tm_mon / 3) + 1;
 					break;
 
 				case DTK_YEAR: