diff --git a/client.go b/client.go
index 68e9580..69faaac 100644
--- a/client.go
+++ b/client.go
@@ -142,10 +142,15 @@ func (c *Client) request(ctx context.Context, method string, urlStr string, quer
 
 		failedAttempts++
 		if failedAttempts == c.maxRetries {
-			return nil, fmt.Errorf("Retry request with 429 response failed after %d retries", failedAttempts)
+			return nil, &RateLimitedError{Message: fmt.Sprintf("Retry request with 429 response failed after %d retries", failedAttempts)}
 		}
 		// https://developers.notion.com/reference/request-limits#rate-limits
-		retryAfter := res.Header["Retry-After"][0]
+		retryAfterHeader := res.Header["Retry-After"]
+		if len(retryAfterHeader) == 0 {
+			return nil, &RateLimitedError{Message: "Retry-After header missing from Notion API response headers for 429 response"}
+		}
+		retryAfter := retryAfterHeader[0]
+
 		waitSeconds, err := strconv.Atoi(retryAfter)
 		if err != nil {
 			break // should not happen
diff --git a/error.go b/error.go
index 15fdf53..4813a23 100644
--- a/error.go
+++ b/error.go
@@ -12,3 +12,11 @@ type Error struct {
 func (e *Error) Error() string {
 	return e.Message
 }
+
+type RateLimitedError struct {
+	Message string
+}
+
+func (e *RateLimitedError) Error() string {
+	return e.Message
+}