diff --git a/svc/product_series_auto_scheduler.go b/svc/product_series_auto_scheduler.go
index 7563fb7..e80e52b 100644
--- a/svc/product_series_auto_scheduler.go
+++ b/svc/product_series_auto_scheduler.go
@@ -14,6 +14,7 @@ import (
 	"sort"
 	"strconv"
 	"strings"
+	"sync"
 	"sync/atomic"
 	"time"
 
@@ -77,6 +78,90 @@ type productSeriesAutoStats struct {
 	Skipped   int
 }
 
+var productSeriesFallbackMu sync.Mutex
+var productSeriesFallbackCachedCode string
+var productSeriesFallbackCachedID int64
+var productSeriesFallbackCachedAt time.Time
+
+func productSeriesFallbackEnabled() bool {
+	// Default on: user explicitly requested "stok var ama seri yoksa 1- ata".
+	raw := strings.TrimSpace(strings.ToLower(os.Getenv("PRODUCT_SERIES_FALLBACK_ON_EMPTY")))
+	if raw == "" {
+		return true
+	}
+	return raw == "1" || raw == "true" || raw == "on" || raw == "yes"
+}
+
+func productSeriesFallbackCode() string {
+	code := strings.TrimSpace(os.Getenv("PRODUCT_SERIES_FALLBACK_SERIES_CODE"))
+	if code == "" {
+		code = "1-"
+	}
+	return code
+}
+
+func productSeriesResolveFallbackSeries(ctx context.Context, pg *sql.DB) (int64, string, error) {
+	if !productSeriesFallbackEnabled() {
+		return 0, "", nil
+	}
+	code := productSeriesFallbackCode()
+	if code == "" {
+		return 0, "", nil
+	}
+
+	productSeriesFallbackMu.Lock()
+	// Cache for a bit to avoid repeated lookups under high throughput.
+	if productSeriesFallbackCachedCode == code && productSeriesFallbackCachedAt.After(time.Now().Add(-10*time.Minute)) {
+		id := productSeriesFallbackCachedID
+		productSeriesFallbackMu.Unlock()
+		return id, code, nil
+	}
+	productSeriesFallbackMu.Unlock()
+
+	var id int64
+	var gotCode string
+	err := pg.QueryRowContext(ctx, `
+SELECT id, COALESCE(code,'')
+FROM dfgrp
+WHERE master='zbggseri'
+  AND COALESCE(is_active, TRUE)=TRUE
+  AND (
+    code = $1
+    OR title = $1
+    OR title LIKE $1 || '%'
+  )
+ORDER BY
+  CASE
+    WHEN code = $1 THEN 0
+    WHEN title = $1 THEN 1
+    ELSE 2
+  END,
+  id
+LIMIT 1
+`, code).Scan(&id, &gotCode)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			// cache negative for a short period too
+			productSeriesFallbackMu.Lock()
+			productSeriesFallbackCachedCode = code
+			productSeriesFallbackCachedID = 0
+			productSeriesFallbackCachedAt = time.Now()
+			productSeriesFallbackMu.Unlock()
+			return 0, code, nil
+		}
+		return 0, code, err
+	}
+	if gotCode != "" {
+		code = gotCode
+	}
+	productSeriesFallbackMu.Lock()
+	productSeriesFallbackCachedCode = code
+	productSeriesFallbackCachedID = id
+	productSeriesFallbackCachedAt = time.Now()
+	productSeriesFallbackMu.Unlock()
+	return id, code, nil
+}
+
 var productSeriesSizeGroups = map[string][]string{
 	"tak":        {"44", "46", "48", "50", "52", "54", "56", "58", "60", "62", "64", "66", "68", "70", "72", "74"},
 	"ayk":        {"39", "40", "41", "42", "43", "44", "45", "46"},
@@ -345,6 +430,35 @@ func productSeriesApplyVariant(ctx context.Context, pg *sql.DB, v productSeriesA
 		return 0, 1, nil
 	}
 	selected := productSeriesSelectRules(v, rules)
+	if len(selected) == 0 {
+		fallbackID, _, err := productSeriesResolveFallbackSeries(ctx, pg)
+		if err != nil {
+			return 0, 1, err
+		}
+		if fallbackID > 0 {
+			// Only apply fallback when the variant has no assignments yet.
+			var exists int
+			checkErr := pg.QueryRowContext(ctx, `
+SELECT 1
+FROM zbggseri
+WHERE mmitem_id=$1
+  AND dim1=$2
+  AND (($3::bigint IS NULL AND dim3 IS NULL) OR dim3=$3::bigint)
+LIMIT 1
+`, mmitemID, dim1ID, nullableInt64ForAuto(dim3ID)).Scan(&exists)
+			if checkErr == nil {
+				// keep existing manual/previous assignment; nothing to do
+				return 0, 0, nil
+			}
+			if checkErr != nil && checkErr != sql.ErrNoRows {
+				return 0, 1, checkErr
+			}
+			// Use the fallback series as the single selected rule.
+			selected = []productSeriesAutoRule{{SeriesID: fallbackID}}
+		} else {
+			return 0, 1, nil
+		}
+	}
 	if !apply {
 		return len(selected), 0, nil
 	}