diff --git a/io.hpp b/io.hpp
index f0e5a2b..9112c1f 100644
--- a/io.hpp
+++ b/io.hpp
@@ -142,9 +142,9 @@ static constexpr uintptr_t PORT_A_DIR_REG_ADDR = DDRA + __SFR_OFFSET;
 static constexpr uintptr_t PORT_A_OUTPUT_REG_ADDR = PORTA + __SFR_OFFSET;
 static constexpr uintptr_t PORT_A_INPUT_REG_ADDR = PINA + __SFR_OFFSET;
 #else
-static constexpr uintptr_t PORT_A_DIR_REG_ADDR = nullptr;
-static constexpr uintptr_t PORT_A_OUTPUT_REG_ADDR = nullptr;
-static constexpr uintptr_t PORT_A_INPUT_REG_ADDR = nullptr;
+static constexpr uintptr_t PORT_A_DIR_REG_ADDR = 0;
+static constexpr uintptr_t PORT_A_OUTPUT_REG_ADDR = 0;
+static constexpr uintptr_t PORT_A_INPUT_REG_ADDR = 0;
 #endif
 
 #ifdef PORT_B_AVAILABLE
@@ -152,9 +152,9 @@ static constexpr uintptr_t PORT_B_DIR_REG_ADDR = DDRB + __SFR_OFFSET;
 static constexpr uintptr_t PORT_B_OUTPUT_REG_ADDR = PORTB + __SFR_OFFSET;
 static constexpr uintptr_t PORT_B_INPUT_REG_ADDR = PINB + __SFR_OFFSET;
 #else
-static constexpr uintptr_t PORT_B_DIR_REG_ADDR = nullptr;
-static constexpr uintptr_t PORT_B_OUTPUT_REG_ADDR = nullptr;
-static constexpr uintptr_t PORT_B_INPUT_REG_ADDR = nullptr;
+static constexpr uintptr_t PORT_B_DIR_REG_ADDR = 0;
+static constexpr uintptr_t PORT_B_OUTPUT_REG_ADDR = 0;
+static constexpr uintptr_t PORT_B_INPUT_REG_ADDR = 0;
 #endif
 
 #ifdef PORT_C_AVAILABLE
@@ -162,9 +162,9 @@ static constexpr uintptr_t PORT_C_DIR_REG_ADDR = DDRC + __SFR_OFFSET;
 static constexpr uintptr_t PORT_C_OUTPUT_REG_ADDR = PORTC + __SFR_OFFSET;
 static constexpr uintptr_t PORT_C_INPUT_REG_ADDR = PINC + __SFR_OFFSET;
 #else
-static constexpr uintptr_t PORT_C_DIR_REG_ADDR = nullptr;
-static constexpr uintptr_t PORT_C_OUTPUT_REG_ADDR = nullptr;
-static constexpr uintptr_t PORT_C_INPUT_REG_ADDR = nullptr;
+static constexpr uintptr_t PORT_C_DIR_REG_ADDR = 0;
+static constexpr uintptr_t PORT_C_OUTPUT_REG_ADDR = 0;
+static constexpr uintptr_t PORT_C_INPUT_REG_ADDR = 0;
 #endif
 
 #ifdef PORT_D_AVAILABLE
@@ -172,9 +172,9 @@ static constexpr uintptr_t PORT_D_DIR_REG_ADDR = DDRD + __SFR_OFFSET;
 static constexpr uintptr_t PORT_D_OUTPUT_REG_ADDR = PORTD + __SFR_OFFSET;
 static constexpr uintptr_t PORT_D_INPUT_REG_ADDR = PIND + __SFR_OFFSET;
 #else
-static constexpr uintptr_t PORT_D_DIR_REG_ADDR = nullptr;
-static constexpr uintptr_t PORT_D_OUTPUT_REG_ADDR = nullptr;
-static constexpr uintptr_t PORT_D_INPUT_REG_ADDR = nullptr;
+static constexpr uintptr_t PORT_D_DIR_REG_ADDR = 0;
+static constexpr uintptr_t PORT_D_OUTPUT_REG_ADDR = 0;
+static constexpr uintptr_t PORT_D_INPUT_REG_ADDR = 0;
 #endif
 
 #undef _SFR_IO8