diff --git a/functions/src/place-bet.ts b/functions/src/place-bet.ts
index d1db82a7..0f5b5473 100644
--- a/functions/src/place-bet.ts
+++ b/functions/src/place-bet.ts
@@ -30,7 +30,7 @@ const bodySchema = z.object({
 
 const binarySchema = z.object({
   outcome: z.enum(['YES', 'NO']),
-  limitProb: z.number().gte(0).lte(1).optional(),
+  limitProb: z.number().gte(0.001).lte(0.999).optional(),
 })
 
 const freeResponseSchema = z.object({