diff --git a/frontend/src/utils/cronPreview.ts b/frontend/src/utils/cronPreview.ts
index 3fa99ae..7ed0e84 100644
--- a/frontend/src/utils/cronPreview.ts
+++ b/frontend/src/utils/cronPreview.ts
@@ -89,6 +89,7 @@ function parseField(field: string, min: number, max: number): number[] | null {
     if (stepMatch) {
       const [, base, stepStr] = stepMatch;
       const step = parseInt(stepStr, 10);
+      if (step <= 0) return range(min, max);
       let start = min;
       let end = max;