diff --git a/tool/genrsa.cc b/tool/genrsa.cc
index f5296ce..4b39401 100644
--- a/tool/genrsa.cc
+++ b/tool/genrsa.cc
@@ -44,7 +44,7 @@
     return false;
   }
 
-  unsigned bits, nprimes;
+  unsigned bits, nprimes = 0;
   if (!GetUnsigned(&bits, "-bits", 2048, args_map) ||
       !GetUnsigned(&nprimes, "-nprimes", 2, args_map)) {
     PrintUsage(kArguments);