diff --git a/scripting/engine_spidermonkey.cpp b/scripting/engine_spidermonkey.cpp
index db48df15de0..959ed856a0d 100644
--- a/scripting/engine_spidermonkey.cpp
+++ b/scripting/engine_spidermonkey.cpp
@@ -166,7 +166,7 @@ namespace mongo {
                 ( (boost::uint64_t)(boost::uint32_t)getNumber( o , "top" ) << 32 ) +
                 ( boost::uint32_t)( getNumber( o , "bottom" ) );
             } else {
-                val = getNumber( o, "floatApprox" );
+                val = (boost::uint64_t) getNumber( o, "floatApprox" );
             }
             return val;
         }