diff --git a/internal/engine.cm b/internal/engine.cm
index e0c7211d..43d13759 100644
--- a/internal/engine.cm
+++ b/internal/engine.cm
@@ -279,8 +279,9 @@ var HEADER = Symbol()
 
 // returns a number between 0 and 1. There is a 50% chance that the result is less than 0.5.
 $_.random = function() {
-  var n = os.random()
-  return n > 100000
+  // os.random() returns a 53-bit integer (uint64 >> 11)
+  // Divide by 2^53 to get a value in [0, 1)
+  return (os.random() / 9007199254740992)
 }
 
 $_.random_fit = os.random