diff --git a/stmhal/boards/CERB40/mpconfigboard.h b/stmhal/boards/CERB40/mpconfigboard.h
index 432e0af79b66d78be763608e30cf97ba88af11ff..414eceb64ad88bce31a259e1f04ebb81c780215a 100644
--- a/stmhal/boards/CERB40/mpconfigboard.h
+++ b/stmhal/boards/CERB40/mpconfigboard.h
@@ -48,6 +48,8 @@
 #define MICROPY_HW_I2C1_SDA (pin_B7)
 #define MICROPY_HW_I2C2_SCL (pin_B10)
 #define MICROPY_HW_I2C2_SDA (pin_B11)
+#define MICROPY_HW_I2C3_SCL (pin_A8)
+#define MICROPY_HW_I2C3_SDA (pin_C9)
 
 // SPI busses
 #define MICROPY_HW_SPI1_NSS  (pin_A4)