diff --git a/journal.go b/journal.go
index 6321e99fa4a579558bd155bbe8564c8edaf5b58a..0c7265ee7533d57568ec97bbd77761542fa93eae 100644
--- a/journal.go
+++ b/journal.go
@@ -6,6 +6,7 @@ package lunatask
 
 import (
 	"context"
+	"fmt"
 	"net/http"
 	"time"
 )
@@ -67,6 +68,10 @@ func (b *JournalEntryBuilder) WithContent(content string) *JournalEntryBuilder {
 // Create sends the journal entry to Lunatask. Returns the created entry's metadata;
 // Name and Content won't round-trip due to E2EE.
 func (b *JournalEntryBuilder) Create(ctx context.Context, c *Client) (*JournalEntry, error) {
+	if b.req.DateOn.IsZero() {
+		return nil, fmt.Errorf("%w: date_on is required", ErrBadRequest)
+	}
+
 	resp, _, err := doJSON[journalEntryResponse](ctx, c, http.MethodPost, "/journal_entries", b.req)
 	if err != nil {
 		return nil, err