diff --git a/js/src/xpconnect/src/xpcconvert.cpp b/js/src/xpconnect/src/xpcconvert.cpp
index a46138bfb241..0f6b745d90e2 100644
--- a/js/src/xpconnect/src/xpcconvert.cpp
+++ b/js/src/xpconnect/src/xpcconvert.cpp
@@ -2109,7 +2109,7 @@ XPCConvert::JSArray2Native(XPCCallContext& ccx, void** d, jsval s,
 #define POPULATE(_mode, _t)                                                  \
     PR_BEGIN_MACRO                                                           \
         cleanupMode = _mode;                                                 \
-        if (capacity > ~(size_t)0 / sizeof(_t) ||                            \
+        if (capacity > PR_UINT32_MAX / sizeof(_t) ||                         \
             nsnull == (array = nsMemory::Alloc(capacity * sizeof(_t))))      \
         {                                                                    \
             if(pErr)                                                         \
diff --git a/js/src/xpconnect/src/xpcjsruntime.cpp b/js/src/xpconnect/src/xpcjsruntime.cpp
index 67625d3b07ff..c7ad2488481d 100644
--- a/js/src/xpconnect/src/xpcjsruntime.cpp
+++ b/js/src/xpconnect/src/xpcjsruntime.cpp
@@ -769,7 +769,7 @@ JSBool XPCJSRuntime::GCCallback(JSContext *cx, JSGCStatus status)
     }
 
     nsTArray<JSGCCallback> callbacks(self->extraGCCallbacks);
-    for (PRInt32 i = 0; i < callbacks.Length(); ++i) {
+    for (PRUint32 i = 0; i < callbacks.Length(); ++i) {
         if (!callbacks[i](cx, status))
             return JS_FALSE;
     }