diff --git a/src/gpio.h b/src/gpio.h
index b632b1b..dbe3e33 100644
--- a/src/gpio.h
+++ b/src/gpio.h
@@ -13,8 +13,8 @@ struct gpio {
   volatile uint32_t ODR;      // Port output data register
   volatile uint32_t BSRR;     // Port bit set/reset register
   volatile uint32_t LCKR;     // Port configuration lock register
-  volatile uint32_t AFRL[2];  // Alternative function low register
-  volatile uint32_t AFRH[2];  // Alternative function high register
+  volatile uint32_t AFRL;     // Alternative function low register
+  volatile uint32_t AFRH;     // Alternative function high register
 };
 
 #define GPIO_BASE_ADDR (0x40020000U)