diff --git a/src/anbox/platform/sdl/platform.cpp b/src/anbox/platform/sdl/platform.cpp
index 9d7c1d57cb039a0ba50169653e8da992c69c4fad..d6b733f40e67887f045c9777ec0492540b0ce6cf 100644
--- a/src/anbox/platform/sdl/platform.cpp
+++ b/src/anbox/platform/sdl/platform.cpp
@@ -298,7 +298,7 @@ void Platform::process_events() {
           break;
         case SDL_TEXTINPUT:
           WARNING("Input Event TEXT=%s TYPE=%d WINDOWID=%d", event.text.text, event.type, event.text.windowID);
-          if (text_input_fliter(event.text.text)) {
+          if (text_input_fliter(reinterpret_cast<unsigned char *>(event.text.text))) {
             send(ime_fd_, event.text.text, strlen(event.text.text), 0);
           }
           break;
@@ -310,7 +310,7 @@ void Platform::process_events() {
   }
 }
 
-bool Platform::text_input_fliter(const char* text) {
+bool Platform::text_input_fliter(const unsigned char* text) {
   return text[0] > 0x7f || (input_flag == 0 &&
           ((text[0] <= 'Z' && text[0] >= 'A') || (text[0] <= 'z' && text[0] >= 'a')));
 }
diff --git a/src/anbox/platform/sdl/platform.h b/src/anbox/platform/sdl/platform.h
index ddeb3e3806ff78e647f3522e2f7c83c5e7b41f81..5a4b5a4cd8e49bfa6c3fa38874e8a5a5ad8ad901 100644
--- a/src/anbox/platform/sdl/platform.h
+++ b/src/anbox/platform/sdl/platform.h
@@ -128,7 +128,7 @@ class Platform : public std::enable_shared_from_this<Platform>,
   int ime_socket_ = -1;
   int input_flag = 0;
   void create_ime_socket();
-  bool text_input_fliter(const char* text);
+  bool text_input_fliter(const unsigned char* text);
 
   int find_touch_slot(int id);
   void push_slot(std::vector<input::Event> &touch_events, int slot);