diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index f71fdeb142..6672b8bae5 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -2563,7 +2563,7 @@ pgstat_bestart(void)
 	beentry = MyBEEntry;
 	do
 	{
-		beentry->st_changecount++;
+		pgstat_increment_changecount_before(beentry);
 	} while ((beentry->st_changecount & 1) == 0);
 
 	beentry->st_procpid = MyProcPid;
@@ -2588,8 +2588,7 @@ pgstat_bestart(void)
 	beentry->st_appname[NAMEDATALEN - 1] = '\0';
 	beentry->st_activity[pgstat_track_activity_query_size - 1] = '\0';
 
-	beentry->st_changecount++;
-	Assert((beentry->st_changecount & 1) == 0);
+	pgstat_increment_changecount_after(beentry);
 
 	/* Update app name to current GUC setting */
 	if (application_name)
@@ -2624,12 +2623,11 @@ pgstat_beshutdown_hook(int code, Datum arg)
 	 * before and after.  We use a volatile pointer here to ensure the
 	 * compiler doesn't try to get cute.
 	 */
-	beentry->st_changecount++;
+	pgstat_increment_changecount_before(beentry);
 
 	beentry->st_procpid = 0;	/* mark invalid */
 
-	beentry->st_changecount++;
-	Assert((beentry->st_changecount & 1) == 0);
+	pgstat_increment_changecount_after(beentry);
 }
 
 
@@ -2666,7 +2664,7 @@ pgstat_report_activity(BackendState state, const char *cmd_str)
 			 * non-disabled state.  As our final update, change the state and
 			 * clear fields we will not be updating anymore.
 			 */
-			beentry->st_changecount++;
+			pgstat_increment_changecount_before(beentry);
 			beentry->st_state = STATE_DISABLED;
 			beentry->st_state_start_timestamp = 0;
 			beentry->st_activity[0] = '\0';
@@ -2674,8 +2672,7 @@ pgstat_report_activity(BackendState state, const char *cmd_str)
 			/* st_xact_start_timestamp and st_waiting are also disabled */
 			beentry->st_xact_start_timestamp = 0;
 			beentry->st_waiting = false;
-			beentry->st_changecount++;
-			Assert((beentry->st_changecount & 1) == 0);
+			pgstat_increment_changecount_after(beentry);
 		}
 		return;
 	}
@@ -2695,7 +2692,7 @@ pgstat_report_activity(BackendState state, const char *cmd_str)
 	/*
 	 * Now update the status entry
 	 */
-	beentry->st_changecount++;
+	pgstat_increment_changecount_before(beentry);
 
 	beentry->st_state = state;
 	beentry->st_state_start_timestamp = current_timestamp;
@@ -2707,8 +2704,7 @@ pgstat_report_activity(BackendState state, const char *cmd_str)
 		beentry->st_activity_start_timestamp = start_timestamp;
 	}
 
-	beentry->st_changecount++;
-	Assert((beentry->st_changecount & 1) == 0);
+	pgstat_increment_changecount_after(beentry);
 }
 
 /* ----------
@@ -2734,13 +2730,12 @@ pgstat_report_appname(const char *appname)
 	 * st_changecount before and after.  We use a volatile pointer here to
 	 * ensure the compiler doesn't try to get cute.
 	 */
-	beentry->st_changecount++;
+	pgstat_increment_changecount_before(beentry);
 
 	memcpy((char *) beentry->st_appname, appname, len);
 	beentry->st_appname[len] = '\0';
 
-	beentry->st_changecount++;
-	Assert((beentry->st_changecount & 1) == 0);
+	pgstat_increment_changecount_after(beentry);
 }
 
 /*
@@ -2760,10 +2755,9 @@ pgstat_report_xact_timestamp(TimestampTz tstamp)
 	 * st_changecount before and after.  We use a volatile pointer here to
 	 * ensure the compiler doesn't try to get cute.
 	 */
-	beentry->st_changecount++;
+	pgstat_increment_changecount_before(beentry);
 	beentry->st_xact_start_timestamp = tstamp;
-	beentry->st_changecount++;
-	Assert((beentry->st_changecount & 1) == 0);
+	pgstat_increment_changecount_after(beentry);
 }
 
 /* ----------
@@ -2839,7 +2833,10 @@ pgstat_read_current_status(void)
 		 */
 		for (;;)
 		{
-			int			save_changecount = beentry->st_changecount;
+			int			before_changecount;
+			int			after_changecount;
+
+			pgstat_save_changecount_before(beentry, before_changecount);
 
 			localentry->backendStatus.st_procpid = beentry->st_procpid;
 			if (localentry->backendStatus.st_procpid > 0)
@@ -2856,8 +2853,9 @@ pgstat_read_current_status(void)
 				localentry->backendStatus.st_activity = localactivity;
 			}
 
-			if (save_changecount == beentry->st_changecount &&
-				(save_changecount & 1) == 0)
+			pgstat_save_changecount_after(beentry, after_changecount);
+			if (before_changecount == after_changecount &&
+				(before_changecount & 1) == 0)
 				break;
 
 			/* Make sure we can break out of loop if stuck... */
@@ -2927,12 +2925,17 @@ pgstat_get_backend_current_activity(int pid, bool checkUser)
 
 		for (;;)
 		{
-			int			save_changecount = vbeentry->st_changecount;
+			int			before_changecount;
+			int			after_changecount;
+
+			pgstat_save_changecount_before(vbeentry, before_changecount);
 
 			found = (vbeentry->st_procpid == pid);
 
-			if (save_changecount == vbeentry->st_changecount &&
-				(save_changecount & 1) == 0)
+			pgstat_save_changecount_after(vbeentry, after_changecount);
+
+			if (before_changecount == after_changecount &&
+				(before_changecount & 1) == 0)
 				break;
 
 			/* Make sure we can break out of loop if stuck... */
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 08925336d1..7285f3ee16 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -16,6 +16,7 @@
 #include "libpq/pqcomm.h"
 #include "portability/instr_time.h"
 #include "postmaster/pgarch.h"
+#include "storage/barrier.h"
 #include "utils/hsearch.h"
 #include "utils/relcache.h"
 
@@ -714,6 +715,12 @@ typedef struct PgBackendStatus
 	 * st_changecount again.  If the value hasn't changed, and if it's even,
 	 * the copy is valid; otherwise start over.  This makes updates cheap
 	 * while reads are potentially expensive, but that's the tradeoff we want.
+	 *
+	 * The above protocol needs the memory barriers to ensure that
+	 * the apparent order of execution is as it desires. Otherwise,
+	 * for example, the CPU might rearrange the code so that st_changecount
+	 * is incremented twice before the modification on a machine with
+	 * weak memory ordering. This surprising result can lead to bugs.
 	 */
 	int			st_changecount;
 
@@ -745,6 +752,43 @@ typedef struct PgBackendStatus
 	char	   *st_activity;
 } PgBackendStatus;
 
+/*
+ * Macros to load and store st_changecount with the memory barriers.
+ *
+ * pgstat_increment_changecount_before() and
+ * pgstat_increment_changecount_after() need to be called before and after
+ * PgBackendStatus entries are modified, respectively. This makes sure that
+ * st_changecount is incremented around the modification.
+ *
+ * Also pgstat_save_changecount_before() and pgstat_save_changecount_after()
+ * need to be called before and after PgBackendStatus entries are copied into
+ * private memory, respectively.
+ */
+#define pgstat_increment_changecount_before(beentry)	\
+	do {	\
+		beentry->st_changecount++;	\
+		pg_write_barrier();	\
+	} while (0)
+
+#define pgstat_increment_changecount_after(beentry)	\
+	do {	\
+		pg_write_barrier();	\
+		beentry->st_changecount++;	\
+		Assert((beentry->st_changecount & 1) == 0);	\
+	} while (0)
+
+#define pgstat_save_changecount_before(beentry, save_changecount)	\
+	do {	\
+		save_changecount = beentry->st_changecount;	\
+		pg_read_barrier();	\
+	} while (0)
+
+#define pgstat_save_changecount_after(beentry, save_changecount)	\
+	do {	\
+		pg_read_barrier();	\
+		save_changecount = beentry->st_changecount;	\
+	} while (0)
+
 /* ----------
  * LocalPgBackendStatus
  *