diff --git a/api/prometheus/v1/api.go b/api/prometheus/v1/api.go
index 857512fb8..b68b69c25 100644
--- a/api/prometheus/v1/api.go
+++ b/api/prometheus/v1/api.go
@@ -1138,6 +1138,9 @@ func (h *apiClientImpl) DoGetFallback(ctx context.Context, u *url.URL, args url.
 		return nil, nil, nil, err
 	}
 	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	// Underlying `net.http` library automatically retries` idempotent requests when connectivity issues are hit.
+	// POST requests are not considered idempotent by default, so we need to explicitly mark them as such.
+	req.Header.Set("Idempotency-Key", "TODO")
 
 	resp, body, warnings, err := h.Do(ctx, req)
 	if resp != nil && (resp.StatusCode == http.StatusMethodNotAllowed || resp.StatusCode == http.StatusNotImplemented) {