diff --git a/src/bin/common/pgsql.c b/src/bin/common/pgsql.c
index 4fe32a084..e981aff89 100644
--- a/src/bin/common/pgsql.c
+++ b/src/bin/common/pgsql.c
@@ -3190,8 +3190,62 @@ parseTimeLineHistory(const char *filename, const char *content,
 
 	system->timelines.count = 0;
 
-	TimeLineHistoryEntry *entry =
-		&(system->timelines.history[system->timelines.count]);
+	/*
+	 * Ensure the history buffer exists and has room for at least lineCount + 1
+	 * entries (all parsed lines plus the tip entry written after the loop).
+	 * We reuse the buffer across calls; realloc only when capacity is tight.
+	 */
+	int needed = lineCount + 1;
+
+	if (system->timelines.history == NULL)
+	{
+		int cap = PG_AUTOCTL_TIMELINES_INITIAL_CAPACITY;
+
+		while (cap < needed)
+		{
+			cap *= 2;
+		}
+
+		system->timelines.history =
+			(TimeLineHistoryEntry *) calloc(cap, sizeof(TimeLineHistoryEntry));
+
+		if (system->timelines.history == NULL)
+		{
+			log_error(ALLOCATION_FAILED_ERROR);
+			free(historyLines);
+			return false;
+		}
+
+		system->timelines.capacity = cap;
+	}
+	else if (system->timelines.capacity < needed)
+	{
+		int cap = system->timelines.capacity;
+
+		while (cap < needed)
+		{
+			cap *= 2;
+		}
+
+		TimeLineHistoryEntry *newHistory =
+			(TimeLineHistoryEntry *) realloc(system->timelines.history,
+											 cap * sizeof(TimeLineHistoryEntry));
+
+		if (newHistory == NULL)
+		{
+			log_error(ALLOCATION_FAILED_ERROR);
+			free(historyLines);
+			return false;
+		}
+
+		memset(newHistory + system->timelines.capacity,
+			   0,
+			   (cap - system->timelines.capacity) * sizeof(TimeLineHistoryEntry));
+		system->timelines.history = newHistory;
+		system->timelines.capacity = cap;
+	}
+
+	TimeLineHistoryEntry *entry = &(system->timelines.history[0]);
 
 	for (lineNumber = 0; lineNumber < lineCount; lineNumber++)
 	{
@@ -3271,7 +3325,7 @@ parseTimeLineHistory(const char *filename, const char *content,
 
 	/*
 	 * Create one more entry for the "tip" of the timeline, which has no entry
-	 * in the history file.
+	 * in the history file. Capacity was pre-checked above to include this slot.
 	 */
 	entry->tli = system->timeline;
 	entry->begin = prevend;
diff --git a/src/bin/common/pgsql.h b/src/bin/common/pgsql.h
index 978f6b172..2b51b2eda 100644
--- a/src/bin/common/pgsql.h
+++ b/src/bin/common/pgsql.h
@@ -193,7 +193,7 @@ typedef struct NodeAddressArray
 #define InvalidXLogRecPtr 0
 #define XLogRecPtrIsInvalid(r) ((r) == InvalidXLogRecPtr)
 
-#define PG_AUTOCTL_MAX_TIMELINES 1024
+#define PG_AUTOCTL_TIMELINES_INITIAL_CAPACITY 16
 
 typedef struct TimeLineHistoryEntry
 {
@@ -203,10 +203,19 @@ typedef struct TimeLineHistoryEntry
 } TimeLineHistoryEntry;
 
 
+/*
+ * TimeLineHistory holds a dynamically-allocated array of timeline history
+ * entries. The history pointer starts as NULL and is allocated on first use
+ * inside parseTimeLineHistory(); subsequent calls reuse the same buffer,
+ * growing it with realloc() when needed. No explicit free is required because
+ * this struct is embedded in long-lived per-process structs (LocalPostgresServer
+ * → ReplicationSource → IdentifySystem) that live for the process lifetime.
+ */
 typedef struct TimeLineHistory
 {
 	int count;
-	TimeLineHistoryEntry history[PG_AUTOCTL_MAX_TIMELINES];
+	int capacity;
+	TimeLineHistoryEntry *history;
 } TimeLineHistory;