diff --git a/core/include/esp/iomux_regs.h b/core/include/esp/iomux_regs.h
index 4ea3be2..2600da9 100644
--- a/core/include/esp/iomux_regs.h
+++ b/core/include/esp/iomux_regs.h
@@ -45,7 +45,7 @@ _Static_assert(sizeof(struct IOMUX_REGS) == 0x44, "IOMUX_REGS is the wrong size"
 #define IOMUX_PIN_FUNC_MASK            0x00001030
 
 /* WARNING: Macro evaluates argument twice */
-#define IOMUX_FUNC(val) (VAL2FIELD(IOMUX_PIN_FUNC_LOW, val) | VAL2FIELD(IOMUX_PIN_FUNC_HIGH, val))
+#define IOMUX_FUNC(val) (VAL2FIELD_M(IOMUX_PIN_FUNC_LOW, val) | VAL2FIELD_M(IOMUX_PIN_FUNC_HIGH, val))
 
 /* WARNING: Macro evaluates argument twice */
 #define IOMUX_FUNC_VALUE(regbits) (FIELD2VAL(IOMUX_PIN_FUNC_LOW, regbits) | FIELD2VAL(IOMUX_PIN_FUNC_HIGH, regbits))