diff --git a/include/modules/upower/upower_tooltip.hpp b/include/modules/upower/upower_tooltip.hpp
index 09f6e60..9f6f16e 100644
--- a/include/modules/upower/upower_tooltip.hpp
+++ b/include/modules/upower/upower_tooltip.hpp
@@ -12,7 +12,7 @@ class UPowerTooltip : public Gtk::Window {
  private:
   typedef std::unordered_map<std::string, UpDevice*> Devices;
 
-  std::string getDeviceIcon(UpDeviceKind& kind);
+  const std::string getDeviceIcon(UpDeviceKind& kind);
 
   Gtk::Box* contentBox;
 
diff --git a/src/modules/upower/upower_tooltip.cpp b/src/modules/upower/upower_tooltip.cpp
index 2bff69c..7ae3e89 100644
--- a/src/modules/upower/upower_tooltip.cpp
+++ b/src/modules/upower/upower_tooltip.cpp
@@ -96,7 +96,7 @@ uint UPowerTooltip::updateTooltip(Devices& devices) {
   return deviceCount;
 }
 
-std::string UPowerTooltip::getDeviceIcon(UpDeviceKind& kind) {
+const std::string UPowerTooltip::getDeviceIcon(UpDeviceKind& kind) {
   switch (kind) {
     case UP_DEVICE_KIND_LINE_POWER:
       return "ac-adapter-symbolic";