diff --git a/Core/memory.c b/Core/memory.c
index ce25b04..a3010b0 100644
--- a/Core/memory.c
+++ b/Core/memory.c
@@ -357,6 +357,10 @@ static uint8_t read_high_memory(GB_gameboy_t *gb, uint16_t addr)
                 if (!gb->cgb_mode && gb->boot_rom_finished) {
                     return 0xFF;
                 }
+                /* TODO: Verify actual access timing */
+                if (gb->vram_read_blocked) {
+                    return 0xFF;
+                }
                 uint8_t index_reg = (addr & 0xFF) - 1;
                 return ((addr & 0xFF) == GB_IO_BGPD?
                        gb->background_palettes_data :
@@ -788,6 +792,10 @@ static void write_high_memory(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
                        is required. */
                     return;
                 }
+                /* TODO: Verify actual access timing */
+                if (gb->vram_write_blocked) {
+                    return;
+                }
                 uint8_t index_reg = (addr & 0xFF) - 1;
                 ((addr & 0xFF) == GB_IO_BGPD?
                  gb->background_palettes_data :