diff --git a/Core/joypad.c b/Core/joypad.c
index 89bcba8..bf3e120 100644
--- a/Core/joypad.c
+++ b/Core/joypad.c
@@ -22,6 +22,13 @@ void GB_update_joyp(GB_gameboy_t *gb)
             for (uint8_t i = 0; i < 4; i++) {
                 gb->io_registers[GB_IO_JOYP] |= (!gb->keys[i]) << i;
             }
+            /* Forbid pressing two opposing keys, this breaks a lot of games; even if it's somewhat possible. */
+            if (!(gb->io_registers[GB_IO_JOYP] & 1)) {
+                gb->io_registers[GB_IO_JOYP] |= 2;
+            }
+            if (!(gb->io_registers[GB_IO_JOYP] & 4)) {
+                gb->io_registers[GB_IO_JOYP] |= 8;
+            }
             break;
 
         case 1: