diff --git a/internal/deck/deck.go b/internal/deck/deck.go
index 6d6f432..4b10739 100644
--- a/internal/deck/deck.go
+++ b/internal/deck/deck.go
@@ -415,7 +415,7 @@ func (d Deck) ValidateWithMaxPages(configuredMaxPages int) error {
 		configuredMaxPages = maxPages
 	}
 	if len(d.Pages) < minPages || len(d.Pages) > configuredMaxPages {
-		return fmt.Errorf("deck must contain %d to %d pages", minPages, configuredMaxPages)
+		return fmt.Errorf("deck must contain %d to %d pages (got %d)", minPages, configuredMaxPages, len(d.Pages))
 	}
 	if d.Pages[0].Variant != "cover" {
 		return fmt.Errorf("first page must use cover variant")
diff --git a/internal/deck/deck_test.go b/internal/deck/deck_test.go
index 53c3cdb..e20bbcf 100644
--- a/internal/deck/deck_test.go
+++ b/internal/deck/deck_test.go
@@ -189,7 +189,7 @@ func TestDeckFromJSONRejectsTooFewPages(t *testing.T) {
 	if err == nil {
 		t.Fatalf("FromJSON() error = nil, want non-nil")
 	}
-	if !strings.Contains(err.Error(), "must contain 3 to 12 pages") {
+	if !strings.Contains(err.Error(), "must contain 3 to 12 pages (got 2)") {
 		t.Fatalf("error = %v", err)
 	}
 }
@@ -207,7 +207,7 @@ func TestDeckFromJSONRejectsThirteenPages(t *testing.T) {
 	if err == nil {
 		t.Fatalf("FromJSON() error = nil, want non-nil")
 	}
-	if !strings.Contains(err.Error(), "deck must contain 3 to 12 pages") {
+	if !strings.Contains(err.Error(), "deck must contain 3 to 12 pages (got 13)") {
 		t.Fatalf("error = %v", err)
 	}
 }