diff --git a/src/node_zlib.cc b/src/node_zlib.cc
index 43de81fa4d2ee6..482375cd6169ba 100644
--- a/src/node_zlib.cc
+++ b/src/node_zlib.cc
@@ -156,7 +156,11 @@ class ZCtx : public AsyncWrap, public ThreadPoolWork {
 
     CHECK_EQ(false, args[0]->IsUndefined() && "must provide flush value");
 
-    unsigned int flush = args[0].As<Uint32>()->Value();
+    Environment* env = ctx->env();
+    Local<Context> context = env->context();
+
+    unsigned int flush;
+    if (!args[0]->Uint32Value(context).To(&flush)) return;
 
     if (flush != Z_NO_FLUSH &&
         flush != Z_PARTIAL_FLUSH &&
@@ -171,8 +175,7 @@ class ZCtx : public AsyncWrap, public ThreadPoolWork {
 
     Bytef* in;
     Bytef* out;
-    size_t in_off, in_len, out_off, out_len;
-    Environment* env = ctx->env();
+    uint32_t in_off, in_len, out_off, out_len;
 
     if (args[1]->IsNull()) {
       // just a flush
@@ -182,18 +185,18 @@ class ZCtx : public AsyncWrap, public ThreadPoolWork {
     } else {
       CHECK(Buffer::HasInstance(args[1]));
       Local<Object> in_buf;
-      in_buf = args[1]->ToObject(env->context()).ToLocalChecked();
-      in_off = args[2].As<Uint32>()->Value();
-      in_len = args[3].As<Uint32>()->Value();
+      in_buf = args[1]->ToObject(context).ToLocalChecked();
+      if (!args[2]->Uint32Value(context).To(&in_off)) return;
+      if (!args[3]->Uint32Value(context).To(&in_len)) return;
 
       CHECK(Buffer::IsWithinBounds(in_off, in_len, Buffer::Length(in_buf)));
       in = reinterpret_cast<Bytef *>(Buffer::Data(in_buf) + in_off);
     }
 
     CHECK(Buffer::HasInstance(args[4]));
-    Local<Object> out_buf = args[4]->ToObject(env->context()).ToLocalChecked();
-    in_off = args[2].As<Uint32>()->Value();
-    in_len = args[3].As<Uint32>()->Value();
+    Local<Object> out_buf = args[4]->ToObject(context).ToLocalChecked();
+    if (!args[5]->Uint32Value(context).To(&out_off)) return;
+    if (!args[6]->Uint32Value(context).To(&out_len)) return;
     CHECK(Buffer::IsWithinBounds(out_off, out_len, Buffer::Length(out_buf)));
     out = reinterpret_cast<Bytef *>(Buffer::Data(out_buf) + out_off);