diff --git a/lib/index.ts b/lib/index.ts
index d426a69..5b65557 100644
--- a/lib/index.ts
+++ b/lib/index.ts
@@ -131,7 +131,7 @@ export function getProcessList(rootPid: number, callback: (processList: IProcess
  * @param callback The callback to use with the returned list of processes
  */
 export function getProcessCpuUsage(processList: IProcessInfo[], callback: (tree: IProcessCpuInfo[]) => void): void {
-  native.getProcessCpuUsage(processList, (processListWithCpu) => callback(processListWithCpu));
+  native.getProcessCpuUsage(processList, callback);
 }
 
 /**
diff --git a/lib/test.ts b/lib/test.ts
index 2436f95..2f31b7c 100644
--- a/lib/test.ts
+++ b/lib/test.ts
@@ -144,6 +144,11 @@ describe('getProcessList', () => {
 });
 
 describe('getProcessCpuUsage', () => {
+  it('should throw on incorrect argument types', done => {
+    assert.throws(() => getProcessCpuUsage('<…>' as any, () => null), /processList.*array/);
+    assert.throws(() => getProcessCpuUsage([], '<…>' as any), /callback.*function/);
+    done();
+  });
 
   it('should get process cpu usage', (done) => {
       getProcessCpuUsage([{ pid: process.pid, ppid: process.ppid, name: 'node.exe' }], (annotatedList) => {
diff --git a/src/addon.cc b/src/addon.cc
index 6fd43fd..cfb4d5d 100644
--- a/src/addon.cc
+++ b/src/addon.cc
@@ -37,12 +37,12 @@ void GetProcessCpuUsage(const Nan::FunctionCallbackInfo<v8::Value>& args) {
   }
 
   if (!args[0]->IsArray()) {
-    Nan::ThrowTypeError("The first argument of GetProcessCpuUsage, callback, must be an array.");
+    Nan::ThrowTypeError("The first argument of GetProcessCpuUsage, processList, must be an array.");
     return;
   }
 
   if (!args[1]->IsFunction()) {
-    Nan::ThrowTypeError("The second argument of GetProcessCpuUsage, flags, must be a function.");
+    Nan::ThrowTypeError("The second argument of GetProcessCpuUsage, callback, must be a function.");
     return;
   }