diff --git a/MainPanel.c b/MainPanel.c
index be59abd3..5a1fe8f5 100644
--- a/MainPanel.c
+++ b/MainPanel.c
@@ -59,7 +59,7 @@ static HandlerResult MainPanel_eventHandler(Panel* super, int ch) {
 
    if (EVENT_IS_HEADER_CLICK(ch)) {
       int x = EVENT_HEADER_CLICK_GET_X(ch);
-      ProcessList* pl = this->state->pl;
+      const ProcessList* pl = this->state->pl;
       Settings* settings = this->state->settings;
       int hx = super->scrollH + x + 1;
       ProcessField field = ProcessList_keyAt(pl, hx);
diff --git a/ProcessList.c b/ProcessList.c
index 2323c99a..457761a2 100644
--- a/ProcessList.c
+++ b/ProcessList.c
@@ -231,7 +231,7 @@ void ProcessList_sort(ProcessList* this) {
 }
 
 
-ProcessField ProcessList_keyAt(ProcessList* this, int at) {
+ProcessField ProcessList_keyAt(const ProcessList* this, int at) {
    int x = 0;
    const ProcessField* fields = this->settings->fields;
    ProcessField field;
diff --git a/ProcessList.h b/ProcessList.h
index 6b075fa7..737fffb3 100644
--- a/ProcessList.h
+++ b/ProcessList.h
@@ -95,7 +95,7 @@ int ProcessList_size(ProcessList* this);
 
 void ProcessList_sort(ProcessList* this);
 
-ProcessField ProcessList_keyAt(ProcessList* this, int at);
+ProcessField ProcessList_keyAt(const ProcessList* this, int at);
 
 void ProcessList_expandTree(ProcessList* this);