diff --git a/source/quickerNES/core/core.hpp b/source/quickerNES/core/core.hpp
index afc13fb..d14792a 100644
--- a/source/quickerNES/core/core.hpp
+++ b/source/quickerNES/core/core.hpp
@@ -138,7 +138,7 @@ class Core : private Cpu
     return 0;
   }
 
-  void open(Cart const *new_cart)
+  const char *open(Cart const *new_cart)
   {
     close();
     init();
@@ -153,7 +153,7 @@ class Core : private Cpu
     if (mapper == nullptr)
     {
       fprintf(stderr, "Could not find mapper for code: %u\n", mapperCode);
-      exit(-1);
+      return "Unsupported mapper";
     }
 
     // Assigning backwards pointers to cartdrige and emulator now
@@ -165,6 +165,8 @@ class Core : private Cpu
     cart = new_cart;
     memset(impl->unmapped_page, unmapped_fill, sizeof impl->unmapped_page);
     reset(true, true);
+
+    return nullptr;
   }
 
   inline void serializeState(jaffarCommon::serializer::Base &serializer) const
diff --git a/source/quickerNES/core/emu.cpp b/source/quickerNES/core/emu.cpp
index ad513c4..a706be2 100644
--- a/source/quickerNES/core/emu.cpp
+++ b/source/quickerNES/core/emu.cpp
@@ -78,16 +78,19 @@ inline void Emu::clear_sound_buf()
   sound_buf->clear();
 }
 
-void Emu::set_cart(Cart const *new_cart)
+const char *Emu::set_cart(Cart const *new_cart)
 {
   auto_init();
-  emu.open(new_cart);
+  const char *error = emu.open(new_cart);
+  if (error) return error;
 
   channel_count_ = Apu::osc_count + emu.mapper->channel_count();
   sound_buf->set_channel_count(channel_count());
   set_equalizer(equalizer_);
   enable_sound(true);
   reset();
+
+  return nullptr;
 }
 
 void Emu::reset(bool full_reset, bool erase_battery_ram)
@@ -167,10 +170,10 @@ const char *Emu::emulate_frame(uint32_t joypad1, uint32_t joypad2, uint32_t arka
 
 // Extras
 
-void Emu::load_ines(const uint8_t *buffer)
+const char *Emu::load_ines(const uint8_t *buffer)
 {
   private_cart.load_ines(buffer);
-  set_cart(&private_cart);
+  return set_cart(&private_cart);
 }
 
 void Emu::write_chr(void const *p, long count, long offset)