diff --git a/MainPanel.c b/MainPanel.c
index ed7f3ad1c3ede1b82f610369997ffe2790834985..708a077553b39f1ceb33a8e735b84bceb807f47d 100644
--- a/MainPanel.c
+++ b/MainPanel.c
@@ -162,7 +162,7 @@ const char* MainPanel_getValue(MainPanel* this, int i) {
    return "";
 }
 
-bool MainPanel_foreachProcess(MainPanel* this, MainPanel_ForeachProcessFn fn, int arg, bool* wasAnyTagged) {
+bool MainPanel_foreachProcess(MainPanel* this, MainPanel_ForeachProcessFn fn, size_t arg, bool* wasAnyTagged) {
    Panel* super = (Panel*) this;
    bool ok = true;
    bool anyTagged = false;
diff --git a/MainPanel.h b/MainPanel.h
index 83253d666d9438cac5c04a6df11b0fc3bd83f48a..f4671f330ad85570dedbac1a12e2ac36f7b9949b 100644
--- a/MainPanel.h
+++ b/MainPanel.h
@@ -34,7 +34,7 @@ int MainPanel_selectedPid(MainPanel* this);
 
 const char* MainPanel_getValue(MainPanel* this, int i);
 
-bool MainPanel_foreachProcess(MainPanel* this, MainPanel_ForeachProcessFn fn, int arg, bool* wasAnyTagged);
+bool MainPanel_foreachProcess(MainPanel* this, MainPanel_ForeachProcessFn fn, size_t arg, bool* wasAnyTagged);
 
 extern PanelClass MainPanel_class;