diff --git a/source/quickerNES/core/cart.hpp b/source/quickerNES/core/cart.hpp
index ccd61f4..75d025c 100644
--- a/source/quickerNES/core/cart.hpp
+++ b/source/quickerNES/core/cart.hpp
@@ -39,7 +39,7 @@ class Cart
   static_assert(sizeof(ines_header_t) == 16);
 
   // Load iNES file
-  void load_ines(const uint8_t *buffer)
+  const char *load_ines(const uint8_t *buffer)
   {
     ines_header_t h;
 
@@ -50,6 +50,9 @@ class Cart
       bufferPos += copySize;
     }
 
+    if (memcmp(h.signature, "NES\x1A", 4) != 0)
+      return "Not an iNES file";
+
     set_mapper(h.flags, h.flags2);
 
     // skip trainer
@@ -73,6 +76,8 @@ class Cart
       memcpy(chr(), &buffer[bufferPos], copySize);
       bufferPos += copySize;
     }
+
+    return nullptr;
   }
 
   inline bool has_battery_ram() const { return mapper & 0x02; }
diff --git a/source/quickerNES/core/emu.cpp b/source/quickerNES/core/emu.cpp
index a706be2..751b12a 100644
--- a/source/quickerNES/core/emu.cpp
+++ b/source/quickerNES/core/emu.cpp
@@ -172,7 +172,9 @@ const char *Emu::emulate_frame(uint32_t joypad1, uint32_t joypad2, uint32_t arka
 
 const char *Emu::load_ines(const uint8_t *buffer)
 {
-  private_cart.load_ines(buffer);
+  const char *error = private_cart.load_ines(buffer);
+  if (error) return error;
+
   return set_cart(&private_cart);
 }
 
@@ -842,4 +844,4 @@ void Emu::RestoreAudioBufferState()
   sound_buf->RestoreAudioBufferState();
 }
 
-} // namespace quickerNES
\ No newline at end of file
+} // namespace quickerNES