diff --git a/src/ria_toolkit_oss_cli/ria_toolkit_oss/capture.py b/src/ria_toolkit_oss_cli/ria_toolkit_oss/capture.py
index ed9f338..00ad5db 100644
--- a/src/ria_toolkit_oss_cli/ria_toolkit_oss/capture.py
+++ b/src/ria_toolkit_oss_cli/ria_toolkit_oss/capture.py
@@ -337,6 +337,8 @@ def capture(
     if duration is not None and num_samples is None:
         num_samples = int(duration * sample_rate)
         echo_verbose(f"Duration {duration}s = {num_samples} samples at {format_sample_rate(sample_rate)}", verbose)
+    elif duration is None and num_samples is None:
+        raise click.ClickException(f"Must provide either --num-samples or --duration")
 
     # Show capture parameters
     echo_progress(f"Capturing from {device.upper()}...", quiet)