diff --git a/nss/makedb.c b/nss/makedb.c
index 8d7d027..fdcf4c6 100644
--- a/nss/makedb.c
+++ b/nss/makedb.c
@@ -591,10 +591,12 @@ copy_valstr (const void *nodep, const VISIT which, const int depth)
 }
 
 
+/* Check if a number is prime.  We check only odd numbers greater than 10.
+   Enter even numbers and watch the function fail in mysterious ways.  Odd
+   numbers less than 10 return false even if they are prime.  */
 static int
 is_prime (size_t candidate)
 {
-  /* No even number and none less than 10 will be passed here.  */
   size_t divn = 3;
   size_t sq = divn * divn;
 
@@ -605,7 +607,7 @@ is_prime (size_t candidate)
       ++divn;
     }
 
-  return candidate % divn != 0;
+  return (candidate >= divn && candidate % divn != 0);
 }